Isolation of the penicillin-binding peptide from D-alanine carboxypeptidase of Bacillus subtilis.

The D-alanine carboxypeptidase of B. subtilis is a membrane-bound enzyme which is inhibited by penicillins and binds them covalently. The enzyme has been labeled with [14C]- or [35S]penicillin. After tryptic or Pronase digestion of the labeled, denatured, reduced, and carboxymethylated enzyme, a radioactive peptide was isolated in each case. The amino acid compositions of these two peptides are reported. The Pronase peptide was a subset of the tryptic peptide. Neither contained a cysteine residue and the only amino acid in the Pronase peptide to which the penicillin could be bound was a serine residue.