Degradation of Neurohypophyseal Hormones by Brain Extracts and Purified Brain Enzymes 1

Abstract

Summary

Rat brain tissue inactivates oxytocin and arginine-vasopressin by the release of the C-terminal dipeptide and glycinamide. Most of the enzymic activities are present in the 100,000g supernatant fraction although some activity is bound to particulates. Extracts prepared in isotonic sucrose exhibit a higher ratio of dipeptide to glycinamide released than do comparable preparations in hypotonic medium. Inactivation of oxytocin is also demonstrated in homogenates of the median eminence region. Purified arylamidase from pig brain inactivates neurohypophyseal hormones negligibly and pig brain aminopeptidase inactivates not at all. It is suggested that enzymes present in brain inactivate neurohypophyseal hormones primarily by hydrolysis of peptide bonds in the acyclic portion, and to a minor degree by initial cleavage of the N-terminal half-cystine residue.

The authors are grateful to Mrs. H. Shlank for excellent technical assistance, and to Dr. M. Pirotta for his contributions in the preliminary phase of this study.