The purification and the amino acid content of vasopressin preparations.

Since the discovery (1) of the pressor activity of extracts of the posterior lobe of the pituitary gland, many laboratories have investigated the fractionation of the extracts obtained from this gland. The physiological potency of various preparations, as well as the methods of fractionation employed, have already been reviewed in considerable detail (24). In the present paper we report a new method of purification of vasopressin’ which has yielded preparations of high potency. A study of the amino acid composition of these preparations is also presented. Earlier investigations have shown the presence of certain amino acids in vasopressin preparations of high potency. In 1933 it was reported that a preparation having a potency of 206 units of pressor activity per mg. contained a relatively large amount of tyrosine and of sulfur (5). Later Irving, Dyer, and du Vigneaud (6), using electrophoretically purified material, found that after preliminary purification the tyrosine and cystine content increased with the pressor potency. They obtained the values 9.9 per cent (tyrosine) and 11.2 per cent (cystine) in their most potent preparation (200 units per mg.). Stehle and Frazer (7) described preparations having a potency of 200 units per mg. which contained 9.5 per cent tyrosine, 7.7 per cent cystine, and 8.9 per cent arginine. They reported that phenylalanine was lacking in their preparations, and that glutamic acid, aspartic acid, and leucine were probably lacking. Later, Stehle and Trister (8) reported the presence of proline and isoleucine in their preparations and the absence of tryptophan, glycine, histidine, and hydroxyproline. More recently Potts and Gallagher (9) reported a prep-