Isolation of a Tridecapeptide from Natriuretic Fractions of Bovine Posterior Pituitary

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Abstract
Crude Van Dyke protein prepared from frozen bovine posterior pituitary glands was treated with formic acid to release small bound and adsorbed peptides. Gel filtration, continuous free‐flow electrophoresis and descending paper electrophoresis were used to separate the small peptides into successively purer fractions which were assayed for pressor, uterotonic, natriuretic and melanocyte stimulating activities under double blind conditions. The highest peak of natriuretic activity was associated with only a small pressor and no uterotonic activities, and the same fractions contained a ninhydrin‐positive spot on paper electrophoresis, the mobility of which at pH 5.6 was similar to that of alpha‐melanocyte stimulating hormone (MSH) and ACTH‐(1–13‐amide)‐tri‐decapeptide (1–13 ACTH‐amide) but differed from vasopressin and oxytocin. Material from this spot had an amino acid composition which corresponded with the first 13 residues of ACTH. Quantitative bioassay of the final fraction in the frog demonstrated a melanotropic activity which, however, was lower than would have been expected for pure alpha‐MSH. The natriuretic activity of the isolated fraction was far higher than the potency of separately administered peptides which might be present: arginine‐vasopressin, alpha‐MSH or 1–13 ACTH. It is suggested that the isolated fraction represents a mixture of alpha‐MSH and 1–13 ACTH, and that alpha‐MSH may be an acetylated end‐product of ACTH cleavage in the pituitary.