The zinc supplement required to achieve the maximum activity of metallo-P-lactamases from 12 Bacteroides fragiZis isolates was investigated. Changes in absorbance of imipenem in a spectrophotometric assay with crude cell extracts were performed in the presence and absence of various concentrations of zinc sulphate. The greatest degree of imipenem hydrolysis was seen with the addition of between 50 and 5 0 0~~ zinc sulphate, and the degree of stimulation of enzyme activity in the strains tested

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... aried six-fold. Increasing the zinc sulphate concentration resulted in inhibition of hydrolysis with extracts of low enzymic activity. These findings indicate the importance of determining the optimal zinc concentration for each strain tested in kinetic studies of metallo-P-lactamases.