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 horinone-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. Some time ago a protein having oxytocic, pressor and antidiuretic activities was isolated from the fresh tissue of bovine pituitary glands. The protein appeared to be homogeneous in the ultracentrifuge and by other physical criteria. The molecular weight was about 30 000 (van Dyke, Chow, Greep & Rothen, 1942). It was recognized that the protein had an unusually high sulphur content (499%) and subsequent work led to the conclusion that all the sulphur was present as cystine disulphide bonds (Block & van Dyke, 1950, 1952).