Trypsin liberates an arginine vasopressin-like peptide and neurophysin from a Mr 20,000 putative common precursor.

Abstract

Although the hypothesis that vasopressin and its associated neurophysin are synthesized together in 1 macromolecular common precursor was put forward more than a decade ago, direct confirmation of this hypothesis has been lacking. A [35S]Cys-labeled putative precursor for vasopressin-related neurophysin (MW 20,000, pI [isoelectric point] 6.1) was isolated from the supraoptic nuclei of rats. This precursor was subjected to limited proteolysis with trypsin which produced a MW 10,000 protein and peptide products. The former was identified as neurophysin on the basis of its pH-dependent affinity for vasopressin and its behavior in isoelectric focusing systems (pI 4.6-4.8). The tryptic peptides proved to be vasopressin-like because they: were rich in cysteine, comigrated with vasopressin on gel filtration columns in 6 M guanidine HCl, bound to a neurophysin-Sepharose affinity column at pH 5.7, and were recognized by antibodies against vasopressin. These data on the MW 20,000, pI 6.1 protein represent direct experimental evidence for a candidate for the common precursor of vasopressin and neurophysin. This common precursor should be called propressophysin.