A method and apparatuses for determining the total content of
proteases by means of measuring their
enzyme activity after previous deinhibition is disclosed. In biological samples, lysosomal
proteases are completely (e.g. in
blood serum) or partly (e.g. in tissue homogenates) inhibited. A method proposed for the deinhibition entails immersing a
solid support material (e.g. nylon or
nitrocellulose) as plastic strip to which is linked, covalently or by adsorption, an inhibitor-binding substance which binds the inhibitor corresponding to the
protease more strongly than the
protease in the sample for measurement. After the deinhibition has taken place, the plastic strip is removed from the liquid sample for measurement, and the sample for measurement is passed on for measurement of the
enzyme activity. Fluorogenic substrates from which the fluorogen 7-amino-4-trifluoromethylcoumarin is eliminated proved to be particularly advantageous for the
activity measurement. These substrates make it possible for the sensitivity on measurement in microtitre plates with a
fluorescence reader to be at least 10 times higher compared with conventional AMC substrates in
blood serum, and thus for the fluorimetric determination of such
enzyme activities in
blood serum to be efficient with this measuring arrangement which is widely used in clinical laboratories.