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J Bacteriol. 1968 January; 95(1): 181-187
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Proteinase Enzyme System of Lactic Streptococci III. Substrate Specificity of Streptococcus lactis Intracellular Proteinase¹

^a Department of Food Science, North Carolina State University, Raleigh, North Carolina 27607

ABSTRACT

The substrate specificity of an intracellular proteinase from Streptococcus lactis was investigated in an effort to understand the role of the enzyme in the cell. Peptides in which the N-terminal residue was glycine were not hydrolyzed by the enzyme (exceptions were glycyl-alanine, glycyl-aspartic acid, and glycyl-asparagine), but the peptide was hydrolyzed if the N-terminal residue was alanine. The enzyme also showed activity toward peptides containing aspartic acid or asparagine. Hydrolysis of only the peptide bonds of alanyl, aspartyl, or asparaginyl residues was confirmed by the action of the enzyme on oxidized bovine ribonuclease A- and B- chain insulin. The N-terminal residues of the peptide fragments liberated were identified. The enzyme attacked both substrates only at alanyl, aspartyl, and asparaginyl residues, releasing these as free amino acids. In addition to alanine, aspartic acid, and asparagine, certain other amino acids were liberated from ribonuclease A, but these were accounted for by the relation of their position to alanine, aspartic acid, and asparagine residues.

² Present address: Department of Nutritional Biochemistry, Himeji Woman's College, Shinzaike, Himeji, Hyogo Prefecture, Japan.

¹ Contribution from the Department of Food Science, North Carolina Agricultural Experiment Station, Raleigh. Published with the approval of the Director of Research as paper no. 2435 of the Journal Series.