Neurophysin, Oxytocin and Vasopressin in Neurosecretory Granules and in Crystalline Complexes

Abstract

Sometime ago it was noticed in this laboratory that neurophysin was composed of several proteins separable by electrophoresis in starch gels.¹ Previously bovine neurophysin had been considered to be a homogeneous protein² which could bind both of the pituitary polypeptide hormones, oxytocin and vasopressin. A complex containing all three constituents isolated by van Dyke and his coworkers³ possessed oxytocic and pressor activities in a ratio of 1:1. Landgrebe, Ketterer and Waring⁴ pointed out that the biological activities of the van Dyke protein corresponded to a complex of a Mole of oxytocin and of vasopressin bound per Mole of protein. The fact that neurophysin was a mixture of proteins was of interest because of evidence for the independent release of oxytocin and vasopressin 5,6. Of this interpretation were to prove correct then the all-or-none nature of neurone activation requires that oxytocin cannot be stored in the same granule as vasopressin. No histological methods for distinguishing oxytocin from vasopressin in neurones exists. A biochemical approach would be the isolation of two kinds of neurosecretory granules, the one containing only oxytocin and the other containing only vasopressin.