Activation of pineal acetyl coenzyme A hydrolase by disulfide peptides

Incubation of pineal acetyl-CoA hydrolase preparations with disulfide peptides activates the enzyme. Activation of somatostatin, the most potent peptide tested, is enhanced at higher pH, indicating that disulfide exchange is probably involved. This interpretation is supported by the observation that activation is reversed by dithiothreitol treatment. The order of potency is somatostatin = [Tyr1]somatostatin greater than or equal to Tyr-somatostatin greater than vasopressin = pressinoic acid = [Arg8]vasotocin greater than oxytocin. Insulin, insulin A, insulin B, and [Asu1,6, Arg8]vasopressin were ineffective. This order of potency is distinctly different from that for the inactivation of pineal N-acetyltransferase (Namboodiri, M. A. A., Favilla, J., and Klein, D. C. (1981) Science 213, 571-573) by these peptides. Examination of the primary structure of the peptides reveals that the above order of potency is consistent with the predictions of the nearest neighbor model as applied to the disulfide group.