Peptide kinetics. Part 11.—Influence of divalent metal ions on rate of reaction of glycyl-glycine in the pH ranges 0.3–1.0 and 3.8–6.0

Abstract

Quantitative studies of the effect of some metal ions on the reaction of glycyl-glycine (gg) in the pH ranges 0.3–1.0 and 3.8–6.0 and temperatures ranging from 364 to 387 K are reported. In the pH range 0.3–1.0, Co(II), Mn(II), Cu (II) and Ni(II) do not affect the rate of hydrolysis of gg. A previous report by Lawrence and Moore that Co(II) increases the rate of hydrolysis by 40–70 % is spurious. In the pH range 3.8–6.0 the metal ions Co(II), Ni(II), Zn(II) and Mn(II) catalyze both hydrolytic cleavage and diketopiperazine formation. The reaction scheme proposed for the metalion-catalyzed hydrolysis requires that the rate of hydrolysis be directly proportional to the metal ion concentration and inversely proportional to the hydrogen ion concentration. The experimental results are in accord with these predictions. There is also evidence that the mechanism for Zn(II)-catalyzed hydrolysis is different from that for the other metal ions.