JBC, Vol. 251, Issue 2, 414-423, Jan, 1976
Purification to homogeneity and properties of two D-alanine carboxypeptidases I From Escherichia coli
T. Tamura, Y. Imae and J. L. Strominger
Three homogeneous preparations of D-alanine carboxypeptidases I have been
obtained from Escherichia coli strain H2143, termed enzymes IA, IB, and IC.
Enzyme IA purified from the membrane after extraction with Triton X-100
appeared on sodium dodecyl sulfate gel electrophoresis to be a polypeptide
doublet whose monomer molecular weights were about 32,000 and 34,000. In
addition to D-alanine carboxypeptidase activity, it catalyzed a
transpeptidase reaction with several substrates, bound [14C]penicillin G,
had a weak penicillinase activity, but was devoid of endopeptidase
activity. Enzyme IB obtained from the membrane after LiCl extraction and
enzyme IC obtained from the supernatant solution were either identical or
extremely similar. They were composed of a single polypeptide whose monomer
molecular weight was about 41,000. In addition to carboxypeptidase
activity, they catalyzed an endopeptidase reaction, had weak penicillinase
activity, and had very poor transpeptidase activity, but did not bind
[14C]penicillin G. Some data relating to the mechanism of catalysis by
these enzymes are described. Their possible physiological role is
discussed.