Fractionation of neurophysin by molecular-sieve and ion-exchange chromatography.

Neurophysin has been separated into seven distinct protein fractions. One of these components had no hormone-binding activity. The fractions that had hormone-binding activity were similar in amino acid composition: their cystine content was in the range 11.5-14.5%. The major component, neurophysin-M, was distinguished from the protein isolated by van Dyke by the presence of methionine and the absence of histidine. Neurophysin-M binds both oxytocin and vasopressin with similar affinities.