A Hg (II) induced conformational change in penicillinase

[Copper II complexes of N-heterocyclic formylisothiosemicarbazones with antimicrobial and beta-lactamase inhibitory activity]

The synthesis of copper(III)-complexes from quinoline-2- or quinoxaline-2-aldehyde-isothiosemicarbazones in pyridine and the elucidation of their structure are described. Some of the new substances exhibit an inhibitory action on growth of gram-positive bacteria, especially Bacillus subtilis (ATCC 6633), furthermore in vitro the beta-lactamase I action is inhibited. Using penicillin-resistant Staphylococci as test strains a strong penicillin-synergistic action was discovered.

Substrate-induced deactivation of penicillinases. Studies of beta-lactamase I by hydrogen exchange

The conformational motility of beta-lactamase I from Bacillus cereus was studied by hydrogen exhange. The time course of the isotopic replacement of peptide hydrogen atoms was followed by 'exchange-in' or 'exchange-out' experiments. Many of the substrates for this enzyme that have o-substituted aromatic or heterocyclic side chains (e.g. methicillin or cloxacillin) are known to effect a decrease in enzymic activity ('substrate-induced deactivation'). There was a marked discontinuity in the exchange-out curve when methicillin or cloxacillin was diffused into the enzyme solution. About one-half of the hydrogen atoms that were probed were affected by the presence of these substrates, and the change in the reactivity of the hydrogen atoms was also large. Substrates that do not bring about deactivation (benzylpenicillin and cephalosporin C) do not affect the hydrogen exchange, nor do reversible competitive inhibitors such as the penicilloic acid or penilloic acid. On the other hand, Zn2+ ions do affect the hydrogen exchange; their effect is similar to that of methicillin or cloxacillin.