Abstract
Some enzymatic properties of purified neutral proteinases I and II from Aspergillus sojae were investigated.
Neutra_??_ proteinase I: The optimum pH for casein digestion was around 7 at 30°C for 10min and the optimum temperature was 55°C at pH 7.3 for 10min in the presence of Ca2-. The enzyme activity was almost completely lost at 55°C, pH 7.3, within 10min, but was stabilized by Ca2+ to some extent. At low temperature, the enzyme was highly stable at the range of pH 3 to 11, and at 49°C the most stable pH was 6 to 7.
Neutral proteinase II: The optimum pH for casein digestion was around 6 at 30°C for 10min and the optimum temperature was 65°C at pH 7.3 for 10min. At low temperature, the enzyme was highly stable at the range of pH 4 to 11 and relatively stable at pH 1 to 2, but unstable at around pH 3. Though the enzyme was remarkably thermostable showing the remaining activity of ca. 80% even by the treatment at 99°C for 10min at pH 7.3, it was very unstable at 75°C. This unstability was considered to be resulted from the autolysis of the enzyme, which was conspicuously observed at pH 3 and pH 9. The presence of Ca2+ accelerated the inactivation of the enzyme.
None of metallic salts tested promoted activities of the both enzymes, but Cu2+, Cd2-, Hg2-, Pb2+ and Sn4+ inhibited markedly neutral proteinase I even at low concentrations. EDTA, iodine and NBS inactivated the both enzymes, whereas sulfhydryl reagents, DFP and potato inhibitor did not affect their activities. Sodium thioglycolate, L-cysteine, KCN, 2-mercaptoethanol and phosphate ions inactivated neutral proteinase I to some extent, but did not neutral proteinase II.
