Penicillin 3-aldehyde is a good substrate and not an inhibitor of β-lactamases A and C

Abstract

Replacement of the 3-carboxylate residue in phenoxymethylpenicillin by an aldehyde group gives a good substrate for E. cloacae P99 P-lactamase with k,,, = 34 s-I, K , = 7.5 x loe5 mol dmP3 and k,,,/K, = 4.5 x lo5 dm3 mol-' s-' at pH 7. With B. cereus 569/H f3-lactamase I as a catalyst, k,,,/K, = 1.87 x lo4 dm3 mol-' s-' at pH 7 and shows a bell-shaped dependence on pH with apparent pK,s of 4.76 and 9.72. Any close proximity between the penicillin 3-aldehyde and a lysine amino group on the protein does not result in iminine formation and inhibition of the enzyme.Paper 5/00873E

pKa, MM, and QM studies of mechanisms of β‐lactamases and penicillin‐binding proteins: Acylation step

“…In contrast, the k cat / K m bell‐shaped pH‐dependence of the catalytic rates for serine β‐lactamases with various substrates shows that the anionic group has a much higher p K a of 4.5–6. Also, the pH profile for class A and C β‐lactamase hydrolysis of the lactone and aldehyde variants of penicillins and cephalosporins still exhibits the same bell‐shape pH dependence as for carboxylate analogs with almost identical values for the p K a of the anionic group 16, 17. This indicates that the carboxylate is not the anionic group seen in the pH profiles.…”

“…These groups effectively remove charge without introducing structural elements, which could cause conformational changes or the reorganization of the active site. As a result, the lactones and aldehydes of β‐lactams are good substrates for class A and C β‐lactamases, with much faster rates of hydrolysis than those of the corresponding carboxylates 15–17. The rate increase for the enzymatic reaction is almost the same as for nonenzymatic reactions—16–130 times 15.…”