Proteinase and Peptidase Activities of Cell-Free Extracts from Mutant Strains of Lactic Streptococci

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Abstract
Cell-free extracts prepared from two lactose-negative, proteinase-negative mutant strains of lactic streptococci, Streptococcus lactis (25Sp), and S. cremoris (KHA2), and the parent strains, S. lactis C2 and S. cremoris (KH), were evaluated for proteinase and peptidase activities. Of the mutant cultures tested, the extract from S. lactis (25Sp) had the highest aminopeptidase activity as determined with the substrates L-lysyl-paranitroanilide, L-leucyl-para-nitroanilide, and L-prolyl-para-nitroanilide. Extract from the same strain also had the highest dipeptidase (DL-alanylglycine and DL-leucylglycine served as substrates) activity when cells were initially grown in a suitable medium with pH maintained at 6 or 6.5 by addition of NH4OH. The cellfree extracts from S. lactis (25Sp) and S. cremoris (KHA2) had higher enzyme activities aminopeptidase, and dipeptidase) and had lower intracellular proteinase activity (N,N-dimethyl casein served as substrate) than did extracts of the parent strains when they were grown at pH 6.5. Electrophoretic patterns of cell-free extracts indicated different bands with various enzyme specificities. Both mutant strains had similar specificity for different aminoacyl-.beta.-naphthylamides. Minor differences were noted for dipeptidase activities.