Affiliation:
1. Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
Abstract
A dipeptidase was purified to homogeneity from a crude cell extract of
Streptococcus cremoris
Wg2 by DEAE-Sephacel column chromatography followed by preparative disc gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 49,000. The dipeptidase is capable of hydrolyzing a range of dipeptides, but not peptides with longer chains. The enzyme was shown to be a metallo-Mn
2+
enzyme with a pH optimum of 8 and a temperature optimum of 50�C. The enzyme is strongly inhibited by thiol-reducing reagents but not by sulfhydryl reagents. Kinetic studies indicated that the enzyme has a relatively low affinity for leucyl-leucine and alanyl-alanine (
K
m
, 1.6 and 7.9 mM, respectively) but can hydrolyze these substrates at very high rates (
V
max
, 3,700 and 13,000 μmol/min per mg of protein, respectively).
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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