Cellular Location and Characteristics of Peptidase Enzymes in Lactic Streptococci

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Abstract
Cell extracts from Streptococcus lactis [a dairy products starter culture] C2 fractionated by differential centrifugation possessed peptidases capable of hydrolyzing a variety of commercial dipeptides and were also active on whole casein as a substrate. Maximum dipeptidase activity for the soluble and ribosome-associated fractions was at pH 8.0 at 37.degree. C. Particulate associated dipeptidase activity was maximal at pH 7.0-8.0. The soluble and ribosome-associated enzymes were most active on alanylglycine while leucyl peptides were the best substrates for the particulate fraction. Activity with glycyl peptides was negligible with all cellular fractions. The presence of whole casein in the growth medium suppressed particulate and ribosome activity and slightly stimulated soluble peptidase and proteinase activity.