A beta-lactamase produced by a penicillin-resistant strain of Serratia marcescens was isolated and purified. The kcat. value for benzylpenicillin was about 5% of that observed for the best cephalosporin substrates. However, the low Km of the penam resulted in a high catalytic efficiency (kcat./Km) and the classification of the enzyme as a cephalosporinase might not be completely justified. It also exhibited a low but measurable activity against cefotaxime, cefuroxime, cefoxitin and moxalactam. Substrate-induced inactivation was observed both with a very good (cephalothin) or a very bad (moxalactam) substrate. The active site was labelled by beta-iodopenicillanate. Trypsin digestion produced a 19-residue active-site peptide whose sequence clearly allowed the classification of the enzyme as a class C beta-lactamase.
Properties of a class C β-lactamase from Serratia marcescens
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B Joris, F De Meester, M Galleni, S Masson, J Dusart, J M Frère, J Van Beeumen, K Bush, R Sykes; Properties of a class C β-lactamase from Serratia marcescens. Biochem J 1 November 1986; 239 (3): 581–586. doi: https://doi.org/10.1042/bj2390581
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