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

Replacement of the 3-carboxylate residue in phenoxymethylpenicillin by an aldehyde group gives a good substrate for E. cloacae P99 -lactamase with kcat= 34 s–1, Km= 7.5 × 10–5 mol dm–3 and kcat/Km= 4.5 × 105 dm3 mol–1 s–1 at pH 7. With B. cereus 569/H -lactamase I as a catalyst, kcat/Km= 1.87 × 104 dm3 mol–1 s–1 at pH 7 and shows a bell-shaped dependence on pH with apparent pKas 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