Interaction between non-classical beta-lactam compounds and the Zn2+-containing G and serine R61 and R39 D-alanyl-D-alanine peptidases

The Zn-contg. D-alanyl-D-alanine carboxypeptidase of Streptomyces albus G was slowly inactivated by 6-aminopenicillanic acid (I), reversibly inhibited by 7-aminocephalosporanic acid (II), and unaffected by mecillinam (III), cefoxitin (IV), quinacillin, quinacillin sulfone, clavulanic acid (V), and N-formimidoylthienamycin (VI). IV and VI, which are potent antibacterial agents, inactivated the serine D-alanyl-D-alanine carboxypeptidase/transpeptidase of Actinomadura R39 (R39 enzyme) and, to a lesser extent, the corresponding serine enzyme of Streptomyces R61 (R61 enzyme). All of the other nonclassical β-lactams tested, including III, were slow inactivators of these serine enzymes. The intermediates formed between I and the R61 and R39 enzymes were long- and short-lived, resp., whereas those formed between II and the same R61 and R39 enzymes were short- and long-lived, resp. Breakdown of the short-lived intermediates thus obtained gave rise to several ninhydrin-pos. degrdn. products. The intermediates formed between V and the serine enzymes were long-lived. With the R39 enzyme, the inactivated complex formed in a 1st step underwent subsequent monomol. rearrangement to give rise to a 2nd species exhibiting a high absorbance at 276 nm.