Tyr-105 is a conserved residue in the Class A beta-lactamases and is in close proximity to the active-site. Tyr-105 in beta-lactamase from Bacillus licheniformis was converted into Phe by site-directed mutagenesis. This mutation caused no significant effect on the structure of the enzyme and had only small effects on the catalytic properties. In particular, in comparison to the wild-type, kcat. for benzylpenicillin was increased slightly, whereas it was decreased slightly for several other substrates. For each substrate examined, Km increased 3-4-fold in the mutant compared with the wild-type enzyme. Examination of the effect of pH on the catalytic reaction revealed only small perturbations in the pK values for the acidic and basic limbs of the kcat./Km pH profiles due to the mutation. Overall effects of the Y105F substitution on the catalytic efficiency for different penicillin and cephalosporin substrates ranged from 14% to 56% compared with the wild-type activity. We conclude that Tyr-105 is not an essential residue for beta-lactamase catalysis, but does contribute to substrate binding.
Research Article|October 15 1994
Effects of site-specific mutagenesis of tyrosine 105 in a class A β-lactamase
W A Escobar;
Biochem J (1994) 303 (2): 555-558.
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W A Escobar, J Miller, A L Fink; Effects of site-specific mutagenesis of tyrosine 105 in a class A β-lactamase. Biochem J 15 October 1994; 303 (2): 555–558. doi: https://doi.org/10.1042/bj3030555
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