96 results about "Lactic dehydrogenase" patented technology

The invention discloses an extraction method of safflower leaf exosome-like nano-vesicles and application of the safflower leaf exosome-like nano-vesicles in preparation of drugs for preventing and treating adriamycin-induced cardiotoxicity, fresh safflower leaves are taken and cleaned, a PBS solution is added for crushing and filtering, filtrate is collected and continuously centrifuged, supernate is taken and subjected to ultracentrifugation, precipitates are collected after centrifugation, and the safflower leaf exosome-like nano-vesicles are obtained; and filtering and sterilizing by using a filter membrane to obtain the safflower leaf exosome-like nano-vesicles. The carthamus tinctorius leaf exosome-like nano-vesicles can significantly improve the heart function of doxorubicin-induced cardiotoxic mice; myocardial injury induced by doxorubicin can be repaired, and myocardial fibrosis induced by doxorubicin can be inhibited; the content of a myocardial injury marker lactic dehydrogenase in body serum can be reduced, a new treatment strategy is provided for preventing and treating adriamycin-induced cardiotoxic diseases, and the application prospect is good.

The invention provides a beta-alanine producing strain as well as a construction method and application thereof. According to the bacterial strain, an acetaldehyde dehydrogenase gene adhE, a lactic dehydrogenase gene ldhA, an acetokinase gene ackA, a pyruvate dehydrogenase gene poxB, a DNA binding transcription inhibition factor coding gene lacI, an aspartate kinase thrA, a pantothenic acid synthase gene panC, an alanine synthesis transaminase gene cycA and an alanine synthesis transaminase gene yfbQ are knocked out from an E.coli W3110 genome, and the bacterial strain is obtained. A phosphoenolpyruvate carboxylase gene ppc, a pyridine nucleotide transhydrogenase coding gene pntAB, an aspartic acid transaminase gene aspC, an aspartic acid decarboxylase gene panD derived from pseudomonas aeruginosa and a beta-alanine transporter gene NCgl0580 derived from corynebacterium glutamicum are integrated at the same time, and the bacillus subtilis is used for producing beta-alanine and has the advantage of high fermentation yield.

The invention discloses combined probiotics for improving sarcopenia as well as a preparation method and application of the combined probiotics, and belongs to the field of probiotics. The invention relates to a combined probiotic for improving sarcopenia. The combined probiotic comprises a lactobacillus reuteri body, a lactobacillus johnsonii body, a lactobacillus fermentum body and a bifidobacterium adolescentis body. The combined probiotics disclosed by the invention can be used for remarkably improving the overall symptoms of sarcopenia model mice, including inhibiting weight loss, constipation symptoms and colonic mucosa destruction, prolonging load swimming time, improving muscle endurance, improving skeletal muscle atrophy, improving the expression of I-type slow muscle fiber protein MyHC I and promoting slow muscle fiber repair, and has the effects of preventing and treating sarcopenia. The invention discloses a probiotic intervention method for treating sarcopenia, which comprises the following steps of: preparing probiotics for treating sarcopenia, reducing the content of inflammatory cytokines in muscular tissues, increasing the content of hepatic glycogen, improving systematic metabolism of mice with sarcopenia and damaged serum markers, including lactic acid, lactic dehydrogenase, creatine kinase, creatinine, alanine transaminase ALT and aspartate transaminase AST, providing a new scheme for probiotic intervention for sarcopenia, and being used for preparing related functional products or intervention means.

Provided are a theanine-producing strain and use thereof in tea fermentation production. A corynebacterium glutamicum is proposed, which includes an alanine decarboxylase CsAlaDC mutant. The theanine-producing strain is obtained by taking the corynebacterium glutamicum as a starting strain, knocking out in sequence an α-ketoglutarate dehydrogenase E1 subunit gene odhA, a glutamate external transporter gene Ncg11221 and a lactate dehydrogenase gene ldh; and / or expressesing a citrate synthase gene gltA, a pyruvate kinase gene pyk and a glutamate dehydrogenase gene gdh; and / or overexpressing an alanine dehydrogenase alaA and integrating a γ-glutamine synthetase GMAS into a cg1960 pseudogene locus of the corynebacterium glutamicum.

The invention discloses a construction method of an escherichia coli mutant for producing succinic acid by fermentation of a synthetic medium. The method comprises the following steps: firstly, knocking out a lactic dehydrogenase gene ldhA, a pyruvate formate lyase gene pflB, a ptsG gene responsible for encoding a phosphotransferase system EIIBC protein, an ethanol dehydrogenase gene adhE, an acetokinase-phosphate transacetylase gene ackA-pta, and a ptsG gene responsible for encoding a phosphotransferase system EIIBC protein in escherichia coli; a phosphoenolpyruvate carboxykinase gene pck from bacillus subtilis is integrated at an SS9 safety site of a strain to obtain escherichia coli ESC6 with high succinic acid yield; and mutating one or more loci in one or more genes of a glucose-transcriptional inhibition factor gene mlc, a nitrate response regulatory factor gene narL and a cyclic adenylate receptor protein gene crp to obtain the escherichia coli mutant capable of producing succinic acid by fermentation of a synthetic culture medium, wherein the one or more loci in one or more genes of the glucose-transcriptional inhibition factor gene mlc, the nitrate response regulatory factor gene narL and the cyclic adenylate receptor protein gene crp are mutated. The strain can be fermented in a synthetic medium to produce succinic acid, so that the fermentation cost is greatly reduced, and the strain has a very wide application prospect.

The invention discloses application of lycium barbarum polysaccharide in preparation of a medicine for inhibiting methylamphetamine-induced nerve injury, and relates to the technical field of biological medicines. It is found and proved that lycium barbarum polysaccharide can inhibit methylamphetamine-induced nerve injury, and the effect is remarkable. From the aspect of cell survival, the survival rate of the microglial cells pretreated by the lycium barbarum polysaccharide after METH stimulation is obviously improved. In the molecular mechanism, the lycium barbarum polysaccharide can effectively lower the protein expression level of the METH-induced pyroptosis marker, the content of inflammatory factors IL-1beta and IL-18 can be reduced, and the release of lactic dehydrogenase is reduced. The result shows that the lycium barbarum polysaccharide can alleviate inflammatory response by inhibiting NLRP3 / ASC pathway mediated microglial cell pyroptosis, thereby inhibiting METH-induced nerve injury. The invention provides a new direction for developing METH neurotoxicity intervention medicines.

The invention relates to the field of biological catalysis, and discloses a method and a device for generating ursodesoxycholic acid through continuous flow catalysis of chenodeoxycholic acid. Comprising the following steps: (1) in the presence of first immobilized cells, carrying out a first catalytic reaction on a reaction system containing chenodeoxycholic acid to obtain a first product, the first immobilized cells expressing 7 alpha-hydroxysteroid dehydrogenase and lactic dehydrogenase; the concentration of the chenodeoxycholic acid in the reaction system is 40 to 70 mM; (2) adjusting the pH value of the first product to 8-9, and then in the presence of a second immobilized cell, carrying out a second catalytic reaction on the first product after the pH value is adjusted to obtain ursodesoxycholic acid, and the second immobilized cell expresses 7 beta-hydroxysteroid dehydrogenase and glucose dehydrogenase. According to the method, the stable activity of a catalytic system is kept, efficient conversion of high-concentration CDCA is achieved, meanwhile, precipitation of 7-KLCA is thoroughly avoided, and the synthesis efficiency, the product purity and the process continuity of UDCA are remarkably improved.

The invention discloses a lactic dehydrogenase LdLDH mutant and application thereof, a wild type LdLDH enzyme derived from Lactobacillus delbrueckii subsp. Bulgaricus is taken as a research object, the amino acid sequence of the wild type LdLDH enzyme is designed and modified to obtain a mutant protein, the mutant protein is named as LdLDH-M, the amino acid sequence of the mutant protein is shown as SEQ ID NO.2, the Tm value of the LdLDH-M is 77.1 DEG C, the Tm value of the LdLDH-M is 77.1 DEG C, and the Tm value of the LdLDH-M is 77.1 DEG C; compared with the wild type LdLDH enzyme, the Tm value of the LdLDH enzyme is increased by 27.4 DEG C, and the enzyme activity of the LdLDH enzyme is increased by 1.4 times. Therefore, compared with the wild type LdLDH enzyme, the LdLDH-M has remarkably improved thermal stability and enzymatic activity, and is more beneficial to widening the application range of the LdLDH-M in the fields of high-temperature biological research, industrial biological catalysis and the like.

The invention relates to application of an asparagine endopeptidase inhibitor in preparation of a medicine for improving insulin resistance. According to the application, starting from inhibiting the aging driving factor AEP, the AEP inhibitor is tried to be applied to the research of insulin resistance for the first time, and the AEP inhibitor is found to be capable of remarkably improving glucose tolerance and insulin sensitivity. Therefore, the invention provides the application of the asparagine endopeptidase inhibitor in preparation of the medicine for improving insulin resistance. Experiments prove that the AEP inhibitor not only can significantly enhance insulin sensitivity of old mice and improve glucose tolerance, but also can reduce serum low-density lipoprotein cholesterol and lactic dehydrogenase levels, shows multiple improvement effects on glucose metabolism and lipid metabolism, and also can be used for preparing the AEP inhibitor. After long-term administration, obvious toxic and side effects are not found in pathological examinations of blood routine examination, urine routine examination, heart, liver, spleen, lung, kidney and other important organs, so that the traditional Chinese medicine composition is proved to have good safety and is suitable for long-term intervention of chronic diseases.

The invention discloses a recombinant bacterium for synthesizing phenyllactic acid as well as a construction method and application thereof, and relates to the technical field of microorganisms. The recombinant strain expresses lactic dehydrogenase, and overexpresses YjbB, MdtF, LapA and / or OrtT. According to the invention, a strain for producing the phenyllactic acid is modified by replacing promoters of yjbB, mdtF, lapA and / or ortT genes with strong promoters and the like, so that the strain overexpresses YjbB, MdtF, LapA and / or OrtT, and the yield of the phenyllactic acid can be obviously improved.

The invention discloses a recombinant bacterium for producing L-lactic acid through co-utilization of glucose and xylose as well as a construction method and application of the recombinant bacterium. The invention relates to the technical field of biology, in particular to recombinant bacteria for producing L-lactic acid through co-utilization of glucose and xylose as well as a construction method and application. Methylglyoxal synthase, and / or pyruvate formate lyase, and / or fumarate reductase and / or L-lactic dehydrogenase in receptor Escherichia coli Rec1.0 are modified to obtain recombinant Escherichia coli, the recombinant Escherichia coli is fermented for 24 h, L-lactic acid is the only metabolite, and the yield reaches 2458 g / L; the consumption rate of xylose is 0.76 g / g DCW / h, the consumption rate of glucose is 0.69 g / g DCW / h, and the consumption rate of total sugar reaches 1.45 g / g DCW / h. The recombinant Escherichia coli constructed by the invention can realize efficient utilization of lignocellulose hydrolysate (containing glucose and xylose), and has a wide application prospect.

The invention discloses a traditional Chinese medicine composition for improving memory and concentration and a preparation method thereof, and relates to the technical field of traditional Chinese medicine formulas. The traditional Chinese medicine composition is prepared from the following raw materials in parts by weight: 12-22 parts of fructus alpiniae oxyphyllae, 15-25 parts of radix astragali, 8-16 parts of ginseng, 10-20 parts of walnuts, 10-20 parts of radix puerariae, 6-14 parts of cornel pulp, 8-18 parts of radix rehmanniae, 10-20 parts of Chinese wolfberry fruits, 15-25 parts of spina date seeds, 8-16 parts of polygala tenuifolia, 6-14 parts of rhizoma acori graminei and 4-10 parts of earthworms. According to the traditional Chinese medicine composition for improving memory and concentration and the preparation method of the traditional Chinese medicine composition, polygala ketone contained in polygala tenuifolia can specifically up-regulate hippocampal BDNF expression and doubly repair memory pathway damage caused by alcohol, volatile asarone in acorus gramineus can penetrate a blood brain barrier, and the volatile asarone is compatible with polygala tenuifolia, so that the nerve stimulation threshold value of a single component can be reduced, the intelligence promoting effect can be improved, and the traditional Chinese medicine composition can be used for improving memory and concentration. The earthworm extract can inhibit the activity of lactic dehydrogenase in the brain, and the synergistic effect mechanism of the polygala tenuifolia, the rhizoma acori graminei and the earthworm can also play a role in preventing and treating the Alzheimer's disease.

The invention belongs to the technical field of biological enzymes, and particularly relates to mutant clostridium sporogenes source phenyllactic dehydrogenase, a method for preparing indole-3-lactic acid from the mutant clostridium sporogenes source phenyllactic dehydrogenase and application of the mutant clostridium sporogenes source phenyllactic The mutant type clostridium sporogenes source phenyllactic acid dehydrogenase comprises N53V mutant type clostridium sporogenes source phenyllactic acid dehydrogenase, R154K mutant type clostridium sporogenes source phenyllactic acid dehydrogenase and N53V / R154K mutant type clostridium sporogenes source phenyllactic acid dehydrogenase. The amino acid sequences of the polypeptide are respectively shown as SEQ ID NO: 6, SEQ ID NO: 10 and SEQ ID NO: 12. Constructing a genetically engineered bacterium for expressing the mutant phenyllactic dehydrogenase in escherichia coli; and tryptophan can be efficiently fermented and catalyzed to be converted into indole-3-lactic acid, and the yield of the indole-3-lactic acid generated by fermentation is increased to 1.85 times, so that the mutant has a very good application prospect in the aspect of fermentation preparation of the indole-3-lactic acid.

The invention relates to the technical field of blood detection, in particular to a formula of an optimized alanine aminotransferase kit, which has the technical scheme that lactic dehydrogenase, NADH (nicotinamide adenine dinucleotide), DCA-Na, glycerol and a Proclin-300 preservative are dissolved in a reagent I Tris buffer solution of the ALT kit; l-alanine, alpha-ketoglutaric acid, glycerol and a Proclin-300 preservative are dissolved in a Tris buffer solution of the reagent II, DCA-Na in the kit is an activator of a pyruvate-lactic dehydrogenase compound and inhibits the kinase activity of pyruvate dehydrogenase, glycerol is an enzyme activity stabilizer, Proclin-300 is a preservative, an instrument is used for detection at the main wavelength of 340 nm and the auxiliary wavelength of 380 nm, and the detection result is accurate. And calculating the ALT activity according to the decreasing rate of NADH (nicotinamide adenine dinucleotide).

The invention discloses a preparation method and application of a lactic dehydrogenase mutant with improved thermal stability. The lactic dehydrogenase mutant is obtained by amplifying a mutation primer by taking a plasmid of wild lactic dehydrogenase as a template; the amino acid sequence of the wild type lactic dehydrogenase is as shown in SEQ ID NO. 1; lactic dehydrogenase mutants M53D and S309P with improved thermal stability are obtained, the residual enzyme activity of the S309P mutant is 76% after the S309P mutant is incubated for 1.5 h at 50 DEG C, and only 50% of the activity of wild type enzyme remains under the same treatment condition.

The invention discloses an application of sodium oxamate in preparation of anti-influenza virus products, and provides an application of sodium oxamate as a lactic dehydrogenase A inhibitor in preparation of anti-influenza virus products, the sodium oxamate has broad-spectrum antiviral activity, and can play a unique action mechanism by regulating host cell metabolism (such as protein lactylation). And a new direction is provided for overcoming virus resistance.

The invention discloses a genetically engineered bacterium for synthesizing N-acetyl blue as well as a construction method and application of the genetically engineered bacterium. The genetically engineered bacterium is prepared by knocking out a lactic dehydrogenase gene ldh and inserting a phosphoketolase gene xfpK on a knockout site, knocking out a pyruvate oxidase gene poxB and inserting a phosphate transacetylase gene pta on a knockout site of a microorganism for producing N-acetyl blue, and knocking out an aconitase inhibition factor gene acnR, inserting a glutamate dehydrogenase gene gdhA on a knockout site, knocking out a glutamine synthetase adenylation transferase gene glnE, and inserting an alpha-ketoglutarate dehydrogenase inhibition factor gene odhI on a knockout site to obtain the strain. According to the method, the supply of the precursor acetyl coenzyme A is enhanced by introducing a non-oxidative glycolysis pathway, the pH dynamic regulation system balances the metabolic flux, and the double breakthrough of the yield and the carbon recovery rate of the N-acetyl blue is realized by combining a two-stage fermentation process.

The present application relates to the application of sulfasalazine combined with lactate dehydrogenase inhibitor in preparing the inhibition of TIF1 gamma lactic acid product, belongs to the field of biological medicine technology. The present application finds that sulfasalazine can block the lactic acidification of the 763th and 769th lysine of transcription intermediate factor 1 gamma (TIF1 gamma), and the combination of sulfasalazine and lactate dehydrogenase inhibitor can strengthen the block of the lactic acidification of the 763th and 769th lysine of transcription intermediate factor 1 gamma, improve the expression level of TIF1 gamma, and then improve the treatment effect on TIF1 gamma related cancer.

The invention discloses a method for detecting the concentration of acetic acid in an anaerobic fermentation system by using a bioelectrochemical sensor, acetic acid is detected by using the bioelectrochemical sensor, the bioelectrochemical sensor comprises a screen-printed electrode, and the working surface of the screen-printed electrode is modified with reduced graphene oxide and polymethylene blue. The working surface of the screen printing electrode is connected with acetokinase, pyruvate kinase and lactic dehydrogenase through a cross-linking agent. According to the method, the adopted sensor has better conductivity, higher response speed and higher current intensity, when the sensor is used for detecting the concentration of acetic acid in a fermentation system, the sensor has the advantages of being easy to operate, low in sample consumption, low in price, high in accurate measurement precision, high in detection speed and the like, and rapid detection of the concentration of acetic acid can be achieved; the acetic acid concentration in the anaerobic fermentation process in different periods can be timely and accurately obtained, effective data can be provided for anaerobic fermentation analysis, and the method has important significance for monitoring the process stability of anaerobic fermentation.

The invention discloses an image processing method and device for judging suspension red blood cell hemolysis. The method comprises the following steps: acquiring a blood image set; the blood image set comprises a plurality of blood images and corresponding label information; acquiring a blood parameter information set; the blood parameter information set comprises a plurality of blood parameters and corresponding label information; the blood parameters comprise hemoglobin concentration, reticulocyte concentration, indirect bilirubin concentration, lactic dehydrogenase concentration and globin concentration; utilizing the blood image set and the blood parameter information set to construct a blood hemolysis composite detection model; based on the blood hemolysis composite detection model, processing the collected blood image and blood parameters to obtain hemolysis detection result information; the hemolysis detection result information is used for representing erythrocyte hemolysis information of the blood corresponding to the collected blood image and blood parameters.

The application discloses genetically engineered bacteria for producing alpha-ketoglutaric acid and application. The genetically engineered bacteria are obtained by weakening the expression of alpha-ketoglutaric acid dehydrogenase gene odhA, weakening the expression of glutamate transporter protein gene cg1434, weakening the expression of glutamate synthase key subunit gene gltB, weakening the expression of lactic acid dehydrogenase gene ldh, weakening the expression of glutamate dehydrogenase gene gdh, weakening the expression of serine / threonine protein kinase gene pknG, enhancing the expression of pyruvate carboxylase gene pyc, introducing and expressing glutamate oxidase gene lgox at the site of lactic acid dehydrogenase ldh gene, and enhancing the expression of strong catalase gene katA on the basis of a Corynebacterium glutamicum starting strain. The genetically engineered bacteria can efficiently produce alpha-ketoglutaric acid under the condition of limited ammonia culture, and have a good application prospect.

This invention discloses the use of polylactic acid (PLA) and its copolymers in the preparation of products that promote hair follicle growth and repair, belonging to the field of biomedical technology. Through in vitro and in vivo experiments, this invention demonstrates that PLA can significantly upregulate the expression of lactate dehydrogenase A and transforming growth factor β2 in dermal papilla cells, promoting dermal papilla cell proliferation and hair follicle growth and damage repair. Based on these findings, this invention provides the application of PLA and its copolymers in the preparation of products that promote hair follicle growth and damage repair, offering a safe and effective treatment strategy for hair follicle-related diseases.

The invention discloses issatchenkia orientalis capable of efficiently synthesizing L-malic acid and application of the issatchenkia orientalis, and belongs to the technical field of biological engineering. In an existing gene edited yeast strain in a laboratory, endogenous lactic dehydrogenase IoLDH2 and IoLDH3 are over-expressed, endogenous IoLDH1 is knocked out, and lactic dehydrogenase EcD-LDH from escherichia coli and lactic dehydrogenase NmD-LDH from neisseria meningitidis are over-expressed. After fermentation for 72 h in a 5 L fermentation tank, the accumulation amount of L-malic acid reaches 296.27 g / L, the yield is 0.97 g / g, the production intensity is 4.11 g / L / h, and the by-product lactic acid is remarkably reduced from 23.56 g / L to 6.7 g / L and is reduced by 71.56%.

The invention belongs to the field of medicines, and relates to a scutellarin aglycone derivative as well as a preparation method and application thereof. The scutellarin aglycone derivative has a structure as shown in a formula I. The preparation method comprises the following steps: reacting scutellarin (a compound II) with methanol to obtain a compound III, then reacting with bornyl chloroacetate (a compound IV) to obtain a compound V, and finally carrying out an alkaline hydrolysis reaction to obtain the compound I, the scutellarin aglycone derivative has the effect of preventing or treating cardiovascular and cerebrovascular related diseases, can improve the activity of superoxide dismutase (SOD), inhibit the production of lactic dehydrogenase (LDH) and reduce the malondialdehyde (MDA) level superior to that of scutellarin, has the inhibiting effect on inflammatory factors TNF-alpha, IL-6 and IL-1beta in cell supernatant superior to that of scutellarin, and can be used for preparing a medicine for treating cardiovascular and cerebrovascular related diseases, such as cardiovascular and cerebrovascular related diseases, cardiovascular and cerebrovascular related diseases, cardiovascular and cerebrovascular related diseases, cardiovascular and cerebrovascular related diseases, cardiovascular and cerebrovascular related diseases, cardiovascular and cerebrovascular related diseases and cardiovascular and cerebrovascular related diseases. The invention has the potential of preparing or preventing cardiovascular and cerebrovascular related diseases.

The invention belongs to the technical field of bioinformatics and medical detection, and particularly relates to a marker combination for neuroblastoma (NB) noninvasive risk level grading, a prediction model, a prediction method and application thereof. The marker combination is used for determining the sex, determining whether the month age is greater than 18 months, determining whether plasma MYCN is amplified, determining whether tumors are metastatic, and determining the content of neuron-specific enolase and lactic dehydrogenase; a machine learning algorithm is used for constructing an NB noninvasive risk degree grading prediction model, the comprehensive performance of the random forest model is optimal, the area value under a subject working characteristic curve reaches 0.956, the sensitivity is 92.9%, the specificity is 82.1%, the accuracy rate is 87.5%, the Kappa value is 0.75, the F1 score is 0.881, and NB middle and low risk patients and NB high risk patients can be effectively distinguished; the NB non-invasive risk level grading prediction model constructed by the invention can quickly, accurately and non-invasively perform NB risk level grading, and has a relatively good clinical application value.

The invention discloses a pharmaceutical composition for preventing and treating inflammatory bowel disease as well as a preparation method and application thereof, and relates to the technical field of modernization of traditional Chinese medicines. The pharmaceutical composition comprises the following active ingredients in parts by weight: 5-30 parts of turmeric, 4-30 parts of green tea, 3-20 parts of liquorice, 5-30 parts of poria cocos and 2-20 parts of cinnamon. The pharmaceutical composition acts on inflammatory factors such as TNF-alpha, IL-1beta and IL-6 by adjusting key signal channels such as NF-kappa B and IL-17, plays a remarkable anti-inflammatory role, has ABTS free radical scavenging and iron ion reducing capabilities, effectively relieves oxidative stress injury caused by inflammation, can remarkably inhibit release of LPS-induced lactic dehydrogenase, and has a remarkable anti-inflammatory effect on inflammatory factors such as TNF-alpha, IL-1beta and IL-6. And the mRNA expression level of the proinflammatory factor is reduced. The invention provides a solid experimental basis and a wide application prospect for developing a safe and efficient inflammatory bowel disease treatment medicine with a clear mechanism.

In Hydrogenophilus bacteria, when one or more of three lactic acid utilizing enzyme genes on the genome of the Hydrogenophilus bacteria is disrupted and a lactate dehydrogenase gene and / or a malate / lactate dehydrogenase gene is introduced thereto, the lactic acid production ability is significantly improved. The inventors of the present invention have identified three lactic acid utilizing enzyme genes of the Hydrogenophilus bacteria. In addition, by introducing a lactate permease gene into the transgenic bacteria, the lactic acid production ability is further improved. The transgenic bacteria of the present invention efficiently produce lactic acid using carbon dioxide as the sole carbon source. That is, the transgenic bacteria can efficiently produce a raw material for biodegradable plastic while solving the global warming problem caused by the increase in carbon dioxide.

The invention discloses an L-lactic dehydrogenase A mutant MALDHAK248A with reduced enzyme activity and an application of the L-lactic dehydrogenase A mutant MALDHAK248A. The mutant MALDHAK248A of the L-lactic dehydrogenase A has an amino acid sequence as shown in SEQ ID NO.3. The invention also discloses a preparation method of the mutant MALDHAK248A. The invention provides a mutant MALDHAK248A of L-lactic dehydrogenase A. The amino acid sequence of the mutant MALDHAK248A is as shown in SEQ ID NO.3. The mutant MALDHAK248A can be used for preparing L-lactic dehydrogenase A. The invention further provides a preparation method of the mutant MALDHAK248A. According to the mutant MALDHAK248A, site-specific mutagenesis is carried out on an amino acid sequence as shown in SEQ ID NO.2, Lys at the 248th site is mutated into Ala, so that the activity of the L-lactic dehydrogenase A is reduced, and the enzyme activity of the L-lactic dehydrogenase A is reduced by 31%. The L-lactic dehydrogenase A mutant MALDHAK248A obtained by the invention can be used as a mutant material capable of remarkably reducing the catalytic activity of an enzyme, and provides reference for further research on the functions of the L-lactic dehydrogenase A.

The present invention relates to an improved process for the preparation of 2, 4-dihydroxybutyrate from a carbon source via homoserine, comprising a two-step route: a first step of catalytically converting the primary amino group of homoserine to a carbonyl group by an enzyme having homoserine transaminase activity as defined by E.C.2. 6. 1.1 or E.C.2. 6. 1.42 or E.C.2. 6. 1.57 to obtain 2-oxo-4-hydroxybutyrate, and a second step of catalytically converting the primary amino group of homoserine to a carbonyl group by an enzyme having homoserine transaminase activity as defined by E.C.2. 6. 1.1 or E.C.2. 6. 1.57 to obtain 2-oxo-4-hydroxybutyrate. And-a second step of catalytically reducing the obtained 2-oxo-4-hydroxybutyrate (OHB) to 2, 4-dihydroxybutyrate by an enzyme having OHB reductase activity, the enzyme having OHB reductase activity being a lactic dehydrogenase as defined by E.C. 1.1. 1.27 or E.C. 1.1. 1.28, or a malate dehydrogenase as defined by E.C. 1.1. 1.37, E.C. 1.1. 1.82, or E.C. 1.1. 1.299, and-a second step of catalytically reducing the obtained 2-oxo-4-hydroxybutyrate (OHB) to 2, 4-dihydroxybutyrate by an enzyme having OHB reductase activity, the enzyme having OHB reductase activity being a lactic dehydrogenase as defined by E.C. 1.1. 1.28, or a malate dehydrogenase as defined by and wherein at least one enzyme having aldolase activity, as defined by E.C.4.1. 2.28, is inactivated to prevent degradation of OHB.