Soil protease is involved in the transformation of amino acids, proteins and other organic compounds
containing protein nitrogen in soil. Its hydrolysate is one of the nitrogen sources of higher plants. Soil acid
protease catalyzes the hydrolysis of protein in acid environment, which is related to soil organic matter
content, nitrogen and other soil properties. Under acid conditions, soil acid protease could hydrolyze casein
to produce tyrosine. In alkaline condition, tyrosine reduced phosphomolybdic acid compound to form
tungsten blue, which has an absorbance peak at 680 nm.
Required reagents and equipment:
Spectrophotometer/Microplate reader, water-bath, adjustable pipette, micro glass cuvette/96 well flat-
bottom plate, methylbenzene, distilled water, 50 meshes sieve.
