Cobalt(III)-ligated peptides as acyl acceptors in peptide synthesis catalyzed by chymotrypsin

The efficiency of cobalt(III)-ligated peptides as acceptor nucleophiles in acyl transfer reactions catalyzed by alpha-chymotrypsin was examined. A series of metallopeptides with the general formula [H-(Gly)n-OCo(NH3)5]2+ (1 < or = n < or = 4) was tested. The aminolysis rate of acyl-chymotrypsin was measured spectrophotometrically by monitoring the concentration of unreacted nucleophile. The rate of the competing hydrolysis of acyl-chymotrypsin was obtained by automatic titration with base, using a pH-stat. The main result was that the positively charged metallopeptides, in general, were more efficient nucleophiles than the corresponding amides and free peptides that were examined for comparison. A binding model that rationalizes the findings is given.