Degradative studies on vasopressin and performic acid-oxidized vasopressin.

Application of the t,echnique of counter-current distribution t,o the purificat,ion of the pressor principle from beef post’erior pituitary glands has afforded preparations with potencies of over 400 pressor units per mg. (1). Analysis of hydrolysates of such preparations for constituent amino acids by chromatography on starch has shown that they contain approximately equimolar amounts of the eight amino acids, phenylalanine, tyrosine, proline, glutamic acid, aspartic acid, glycine, arginine, and cystine, and approximately 3 moles of ammonia per mole of any one amino acid.’ Traces of ot)her amino acids, including leucine and isoleucine, could also be detected. In one instance (3) a vasopressin preparation was obtained which consistently showed about 600 units per mg. in both the pressor and the antidiuretic assays. A hydrolysate of this preparation contained the eight amino acids listed above, but no detectable amounts of any other amino acids. It was of particular significance that no leucine or isoleucine was detectable, which indicated that the preparation was free of oxytocin and that the oxytocic activity of vasopressin represented an inherent biological property (3). A number of samples of vasopressin, prepared by the above procedures and giving equally good amino acid analyses, have shown 400 to 500 pressor units per mg. The lower potencies of such preparations might be due to