Abstract
Exposure of cobalt (II) carboxypeptidase A α, [(CPD)Co(II)], to small molar excesses of the oxidizing agent m-chloroperbenzoate rapidly destroys (< 30 sec) both its peptidase and esterase activities in parallel. Concomitantly, the characteristic Co(II) electron paramagentic resonance (EPR) signal is abolished. [(CPD)Co(III)], isolated from the reaction mixture, has the same molecular weight and amino acid composition as [(CPD)Co(II)], contains 0.95 g-atom of Co and 0.01 g-atom of Zn per mole of protein, does not exhibit an EPR spectrum and is catalytically completely inactive towards both peptide and ester substrates. Identical treatment of the native zinc enzyme affects neither its catalytic activity nor its metal content. The reaction of m-chloroperbenzoate with [(CPD)Co(II)] follows saturation kinetics and is prevented by the inhibitor β-phenylpropionate. Furthermore, under the conditions found to oxidize [(CPD)Co(II)] effectively, there is no reaction with Co(II) E. coli alkaline phosphatase. Thus, m-chloroperbenzoate has the characteristics of an active-site directed oxidizing reagent for [(CPD)Co(II)].
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