Interaction between beta-lactam antibiotics and exocellular DD-carboxypeptidase-transpeptidase of Streptomyces R61

in European Journal of Biochemistry (1974), 50(1), 203-214

On the basis of steady-state kinetics, inhibition of the exocellular dd-carboxypeptidase-trans-peptidase of Streptomyces R61 by β-lactam antibiotics was competitive with regard to the donor substrate ... [more ▼]

On the basis of steady-state kinetics, inhibition of the exocellular dd-carboxypeptidase-trans-peptidase of Streptomyces R61 by β-lactam antibiotics was competitive with regard to the donor substrate. However, the complexes formed between the Streptomyces R61 enzyme and various β-lactam antibiotics were relatively stable, exhibiting half-lives of 40 to 80 min at 37°C and neutral pH. During breakdown of the complexes the protein underwent reactivation, whereas the released antibiotic molecule was chemically altered. With [14C]benzylpenicillin, the released compound was neither benzylpenicillin nor benzylpenicilloic acid. The properties of the Streptomyces R61 enzyme β-lactam antibiotic complexes were compared with those of the complexes formed between the same antibiotics and either the membrane-bound transpeptidase from Streptomyces R61 or the exocellular dd-carboxypeptidase-transpeptidase of Streptomyces R39. [less ▲]

Membrane-bound DD-carboxypeptidase and LD-transpeptidase of Streptococcus faecalis ATCC 9790

in European Journal of Biochemistry (1974), 44(2), 459-468

Isolated membranes of Streptococcus faecalis ATCC 9790 exhibit DD-carboxypeptidase activity (standard reaction: Ac2-l-Lys-d-Ala-d-Ala →d-alanine + Ac2-l-Lys-d-Ala) and ld-trans-peptidase activity ... [more ▼]

Isolated membranes of Streptococcus faecalis ATCC 9790 exhibit DD-carboxypeptidase activity (standard reaction: Ac2-l-Lys-d-Ala-d-Ala →d-alanine + Ac2-l-Lys-d-Ala) and ld-trans-peptidase activity (standard reaction: Ac2-l-Lys-d-Ala + acceptor →d-alanine + Ac2-l-Lys-acceptor). The DD-carboxypeptidase activity has a considerable specificity for peptides with a C-terminal l-R3-d-Ala-d-Ala sequence where R3 is an amino acid residue and a long side-chain at the l-R3 position. A corresponding DD-transpeptidation reaction yielding the product Ac2-l-Lys-d-Ala-d-[14C]Ala from the system Ac2-l-Lys-d-Ala-d-Ala-f-d-[14C] alanine was not detected. The ld-transpeptidase activity has a considerable specificity for peptide donors that have an Nα-substituted, C-terminal l-R3-d-Ala sequence with a free ω-amino group at the end of a long side-chain at the l-R3 position, and a considerable specificity for amino group acceptors that are located on a d-carbon in α-position to a free carboxyl group. In the absence of acceptor, hydrolysis of the dipeptide Ac2-l-Lys-d-Ala (ld-carboxypeptidase activity) was not observed. Both DD-carboxypeptidase and ld-transpeptidase activities are inhibited by β-lactam antibiotics, but their relative sensitivity differs according to the particular antibiotic used. [less ▲]

Kinetics of concomitant transfer and hydrolysis reactions catalysed by the exocellular DD-carboxypeptidase-transpeptidase of streptomyces R61

in Biochemical Journal (1973), 135(3), 483-492

When Ac(2)-l-Lys-d-Ala-d-Ala and either meso-diaminopimelic acid or Gly-l-Ala are exposed to the exocellular dd-carboxypeptidase-transpeptidase of Streptomyces R61, transpeptidation reactions yielding Ac ... [more ▼]

When Ac(2)-l-Lys-d-Ala-d-Ala and either meso-diaminopimelic acid or Gly-l-Ala are exposed to the exocellular dd-carboxypeptidase-transpeptidase of Streptomyces R61, transpeptidation reactions yielding Ac(2)-l-Lys-d-Ala-(d)-meso- diaminopimelic acid and Ac(2)-l-Lys-d-Ala-Gly-l-Ala occur concomitantly with the hydrolysis of the tripeptide into Ac(2)-l-Lys-d-Ala. The proportion of the enzyme activity which can be channelled in the transpeptidation and the hydrolysis pathways depends upon the pH and the polarity of the environment. Transpeptidation is favoured both by increasing the pH and by decreasing the water content of the reaction mixtures. Kinetics suggest that the reactions proceed through an ordered mechanism in which the acceptor molecule (meso-diaminopimelic acid or Gly-l-Ala) binds first to the enzyme. Both acceptors behave as non-competitive inhibitors of the hydrolysis pathway. Transpeptidation is inhibited by high concentrations of Gly-l-Ala but not by high concentrations of meso-diaminopimelic acid. The occurrence on the enzyme of an additional inhibitory binding site for Gly-l-Ala is suggested. [less ▲]

Fluorescence and circular dichroism studies on the Streptomyces R61 DD-carboxypeptidase-transpeptidase. Penicillin binding by the enzyme

in Biochemical Journal (1973), 135(3), 493-505

The circular dichroism of the dd-carboxypeptidase-transpeptidase from Streptomyces R61 shows in the near u.v. a set of weak extrema at 289nm (positive) and at 282, 275 and 268nm (all negative). In the far ... [more ▼]

The circular dichroism of the dd-carboxypeptidase-transpeptidase from Streptomyces R61 shows in the near u.v. a set of weak extrema at 289nm (positive) and at 282, 275 and 268nm (all negative). In the far u.v. it shows negative extrema at 217-218 and 208nm, crossover at 202nm and a positive maximum at about 194nm. The u.v. absorption of the enzyme shows it to contain tyrosine and tryptophan in approx. 3.4:1 ratio. The enzyme is fluorescent with a maximum emission at 318-320nm. The near-u.v. circular dichroism of the protein is extensively affected by binding of penicillin G, but the far u.v. is unaffected. Binding of the antibiotic also causes quenching of the fluorescence of the enzyme. The latter effect has been used to study the binding of penicillin G to the enzyme and the influence exerted upon it by salts, denaturants and peptide substrates and inhibitors. High-affinity binding of penicillin appears to be comparatively slow and reversible, and can occur under conditions in which the protein is enzymically inactive. The thermal denaturation of the enzyme in guanidinium chloride at pH7 is affected by binding of the antibiotic. The presence of even large concentrations of beta-mercaptoethanol neither impaired the activity of the enzyme nor prevented its inhibition by penicillin G or cephalosporin C. A new hypothesis for the molecular mechanism of the interaction of the enzyme with penicillin is proposed. [less ▲]

DD-carboxypeptidase-transpeptidase and killing site of beta-lactam antibiotics in Streptomyces strains R39, R61, and K11

in Antimicrobial Agents and Chemotherapy (1973), 3(2), 181-187

Additional evidence is given that in Streptomyces strains R39, R61, and K11 the same enzyme performs dd-carboxypeptidase and transpeptidase activities and that this enzyme is the killing site of beta ... [more ▼]

Additional evidence is given that in Streptomyces strains R39, R61, and K11 the same enzyme performs dd-carboxypeptidase and transpeptidase activities and that this enzyme is the killing site of beta-lactam antibiotics. With strain R61, it was found that the exocellular enzyme has a sensitivity towards some antibiotics different from that of the membrane-bound enzyme. Under the growth conditions used in the present investigations, beta-lactamase activity was not involved in susceptibility to beta-lactam antibiotics. [less ▲]