Carbon-13 nuclear magnetic resonance studies of the interaction of specifically labeled (90%- 13C) oxytocin and arginine vasopressin with neurophysins

Abstract

Oxytocin and arginine vasopressin have been synthesized, via solid phase techniques, enriched to 90% 13C in the 2-carbon of their C-terminal glycinamide residues. In the presence of an approximately equimolar amount of bovine neurophysin II, the 13C nuclear magnetic resonance signal due to the enriched carbon in oxytocin shows a broadening which is highly dependent on both the temperature and the concentration of the neurophysin-oxytocin complex. The linewidth varies from 3 hz, observed at a protein concentration of 11mg/ml and a temperature of 37°, to 120 hz for a protein concentration of 65 mg/ml at 6°C. Similar results were obtained with arginine vasopressin. The results indicate that under conditions of low protein concentration and high temperature, the glycinamide residues of oxytocin and arginine vasopressin bound to neurophysin possess significant internal motion, while lowering the temperature and/or raising the protein-hormone concentration reduces this internal motion, probably concommitant with association of the protein-hormone complex into higher molecular weight aggregates.