Partial purification and properties of proteases from defatted soybean flour.

Abstract
Four chromatographically different proteases were partially purified from defatted soybean flour and their pH optima were around 5.0-5.6 using casein as the substrate. These soybean proteases were designated S1, S2, S3 and S4 according to their order of elution from a DEAE-cellulose column. Each gave a single peak of caseinolytic activity on a Sephadex G-200 column chromatogram and corresponded to MW of about 50,000(S1), 35,000(S2), 60,000(S3) and 200,000(S4). The proteases could hydrolyze casein and poly-Glu. .alpha.-Casein was more rapidly hydrolyzed than .beta.-casein, but the esters or dipeptide could not be hydrolyzed. Aliquots of 10-3 M Hg2+, Cu2+ and Zn2+ inhibited the caseinolytic activities by 70-90%, while other cations, Mn2+, Mg2+, Ca2+ and Ni2+, at the same concentration did not. Proteases S1, S2, S3 and S4 from defatted soybean flour can apparently be classified as acid proteases.

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