1. 1.|Extracellular alkaline proteinases from the molds Aspergillus flavus, Aspergillus oryzae, Aspergillus sojae and Aspergillus sulphureus, isolated and characterized by individual authors in four different laboratories, have been compared using uniform methods under identical conditions in one of our laboratories. 2. 2.|The enzymes studied were compared by gel filtration, disc electrophoresis, amino acid analysis, determination of the pH optima of their proteolytic activity, estimation of their specificity by cleavage of the B-chain of oxidized insulin, and by peptide maps of the tryptic, chymotryptic, and peptic digests of the inactivated proteinases. 3. 3.|The results of this comparison led to the following conclusion: Alkaline proteinases from A. flavus and A. oryzae are probably indentical (or very closely related), alkaline proteinase from A. sojae is closely related but not identical, alkaline proteinase from A. sulphureus is homologous yet less related. 4. 4.|The combination of methods used in this study requires only small quantities of enzymes. It is therefore suitable for preliminary comparison of proteinases and for studies on the degree of their homology.
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