title: Delta 2- and delta 3-cephalosporins, penicillinate and 6-unsubstituted penems. Intrinsic reactivity and interaction with beta-lactamases and D-alanyl-D-alanine-cleaving serine peptidases.
abstract: The intrinsic reactivity of delta 2- and delta 3-deacetoxy-7-phenylacetamidocephalosporanates, penicillanate, unsubstituted, 2-methyl- and 2-phenyl-penems and other beta-lactam antibiotics has been expressed in terms of the second-order rate constant (M-1.s-1(OH-)) for the hydrolysis of the beta-lactam amide bond by OH- at 37 degrees C. The values thus obtained have been compared with the second-order rate constants (M-1.s-1(enzyme) for the opening of the same beta-lactam amide bond during interaction with the beta-lactamases of Streptomyces albus G and Actinomadura R39 and the D-alanyl-D-alanine-cleaving serine peptidases of Streptomyces R61 and Actinomadura R39. Depending on the cases, the accelerating effect due to enzyme action and expressed by the ratio M-1.s-1(enzyme)/M-1.s-1(OH) varies from less than 2 to more than 1 x 10(6). The primary parameter that governs enzyme action is the goodness of fit of the beta-lactam molecule to the enzyme cavity rather than its intrinsic reactivity. With the D-alanyl-D-alanine-cleaving serine peptidases, the three penems studied form intermediate complexes characterized by very short half lives of 14-100 s, values significantly lower than those exhibited by most beta-lactam compounds.
mesh_terms: D000191:Actinomycetaceae / Q000201:enzymology; D000577:Amides; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D002268:Carboxypeptidases / Q000378:metabolism*; D002511:Cephalosporins / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D006868:Hydrolysis; D007700:Kinetics; D010406:Penicillins / Q000378:metabolism*; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; D013302:Streptomyces / Q000201:enzymology; D013329:Structure-Activity Relationship; D001618:beta-Lactamases / Q000378:metabolism*; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000577:Amides; D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D010406:Penicillins; D047090:beta-Lactams; D002268:Carboxypeptidases; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; D001618:beta-Lactamases