On the Streptomyces albus G DD carboxypeptidase mechanism of action of penicillin, vancomycin, and ristocetin

The activity of the D-alanyl-D carboxypeptidase from the penicillin-resistant Streptomyces albus G is not or very little affected by penicillins and related antibiotics. The molecular basis for the mechanism of action of penicillin is discussed. The Streptomyces albus G D-alanyl-D carboxypeptidase appears as a model for the study of a mechanism of penicillin resistance that does not involve the enzymatic degradation of the antibiotic. Vancomycin and ristocetin are shown to inhibit the hydrolysis of sensitive peptides by the Streptomyces albus G D-alanyl-D carboxypeptidase and the mechanism of inhibition is discussed

Enzymes involved in wall peptide crosslinking in Escherichia coli K12, strain 44

By using the glutamate-amidated tetrapeptide l-alanyl-d-isoglutaminyl-(l)-meso-diamino-pimelyl-(l)-d-alanine as a probe, there appears to exist in the membranes of Escherichia coli K12 strain 44 a dd-carboxypoptidase-transpeptidase system which does not recognize this peptide and a dd-carboxypoptidase-transpeptidase system which recognizes it. The dd-carboxypeptidase-endopeptidase system is essentially hydrolytic. It catalyzes the hydrolysis of UDP-N-acetyl-muramyl-pentapeptide into UDP-N-acetylmuramyl-tetrapeptide and the hydrolysis of the wall peptidoglycan peptide dimer into monomers. These activities are not inhibited by the glutamate-amidated tetrapeptide. The system may consist either of two enzyme proteins having predominantly carboxypeptidase activity and endopeptidase activity, respectively, or of one enzyme protein of which the functioning would depend upon the environmental conditions. The dd-carboxypeptidase-transpeptidase system (a) catalyzes concomitant hydrolysis (carboxypeptidase activity) and transfer (natural model transpeptidase activity) reactions with the pentapeptide l-alanyl-γ-d-glutamyl-(l)-meso-diaminopimelyl-(l)-d-alanyl-d-alanine. The transfer reaction leads to the synthesis of a dimer that is identical to the one which occurs in the E. coli wall peptidoglycan; (b) utilizes the glutamate-amidated tetrapeptide as an acceptor. Simultaneous exposure of the pentapeptide and the glutamate-amidated tetrapeptide to the enzyme system leads to the formation of an hybrid monoamidated peptide dimer and causes a decreased hydrolysis of the pentapeptide; (c) by virtue of its own carboxypeptidase activity, it appears to exert some endopeptidase activity. Both carboxypeptidase and endopeptidase activities of this system are inhibited by the glutamate-amidated tetrapeptide, but this represents only a small fraction of the total hydrolytic activity of the membrane Brij-36T extract. (d) The system catalyzes an unnatural model transpeptidation reaction in which glycine replaces d-alanine at the C-terminal position of the nucleotide UDP-N-acetylmuramyl-pentapeptide. This system may also consist either of two enzyme proteins having predominantly natural model transpeptidase activity and unnatural model transpeptidase activity, respectively, or of one enzyme protein of which the functioning would depend upon the environmental conditions. Whatever the exact situation, the E. colidd-carboxypeptidase-transpeptidase system is in many respects, similar to the dd-carboxy-peptidase-transpeptidase single polypeptide enzymes isolated from Streptomyces strains R39 and R61

LL-diaminopimelic acid containing peptidoglycans in walls of Streptomyces sp. and of Clostridium perfringens (type A).

In a major part of the wall peptidoglycans of Streptomyces sp. and of Clostridium perfringens, L-alanyl-D-isoglutaminyl-(L1)-LL-diaminopimelyl-(L1)-D-alanine peptides are cross-linked via D-alanylglycyl-(L2)-LL-diaminopimelic acid linkages (peptidoglycan of the chemotype II group). The Myxobacter AL-I endopeptidase hydrolyzes both D-alanyl-glycine and glycyl-LL-diaminopimelic acid linkages in the walls of C. perfringens, liberating free glycine. In contrast, the Myxobacter AL-I endopeptidase hydrolyzes only D-alanyl-glycine linkages in walls of Streptomyces sp. and the liberation of the glycine residues requires subsequent treatment with an aminopeptidase. No explanation for this observation can be proposed at this time. A minor component of the AL-I endopeptidase hydrolysate of the Streptomyces and C. perfringens walls is a resistant peptide dimer. Analyses indicate that the cross-link in this dimer may be mediated through LL-diamino-pimelylglycyl-LL-diaminopimelic acid linkages. The C termini of the peptide moieties in the wall peptidoglycans are either D-alanine or LL-diarninopimelic acid but never D-alanyl-D-alanine, thus indicating the presence in these microorganisms of carboxypeptidases similar to those of Escherichia coli