Abstract
The alkaline proteinase from Aspergillus sydowi was markedly protected from inactivation by the presence of Ca++ in the enzyme solution. The protective effect of Ca++ was influenced remarkably by the pH values of the enzyme solution, i.e., optimum concentrations of Ca++ for the protective effect at pH 7.1, 7.5 and 7.8 were 10-2, 10-3 and 10-4M, respectively. Conversely, at higher pH values such as 9.0, Ca++ accelerated the rate of inactivation. There was a parallelism between the loss in activity and the increase in ninhydrin-positive material in the enzyme solution.
The proteinase acted on various denaturated proteins, but not on native proteins. In digestion of casein by the proteinase, 92% of nitrogen was turned into soluble form in 0.2M trichloroacetic acid solution, with 14_??_17% of peptide bonds being hydrolyzed. Casein hydrolyzed with the Asp. sydowi proteinase was further hydrolyzed by Pen. chryso-genum, B. subtilis or St. griseus proteinases, which further increased the free amino residues in the reaction mixtures. On the contrary, the Asp. sydowi proteinase reacted only slight-ly on casein hydrolyzed by the above-mentioned proteinases.
