A reversible inhibitor of β-lactamase I from Bacillus cereus

α-Methyl (3S,5R,6R)benzylpenicilloate is a reversible competitive inhibitor of β-lactamase l from Bacillus cereus; the inhibition constant Ki is 6.38 × 10–4M and is independent of pH between pH 5 and 8 which is compatible with binding of the free base form of the thiazolidine residue to the enzyme.