Isolation and Characterization of a Hormone-binding Polypeptide from Pig Posterior Pituitary Powder

Abstract

A large polypeptide has been isolated from acetone powder of pig posterior pituitary tissue by the methods of percolation, gel filtration on Sephadex G-25 and G-50, and ion exchange chromatography on diethylaminoethyl cellulose. The purified polypeptide appears to be homogeneous by the criteria of electrophoresis on paper and starch gel, column and paper chromatography, ultracentrifugation, and amino acid analysis. It consists of 89 amino acid residues with a molecular weight of 9170. The purified peptide contains all of the usual amino acids except histidine and tryptophan. There are 14 glycyl, 13 glutamyl, 7 seryl, 7 alanyl, 7 leucyl, 6 prolyl, 6 cystinyl, 5 argininyl, 5 aspartyl, 3 phenylalanyl, and 1 or 2 of each of the other residues. Its isoelectric point is estimated to be about pH 5.8. It is devoid of pressor and oxytocic activity but has the ability to bind lysine vasopressin, oxytocin, and synthetic analogues of oxytocin. However, the performic acid-oxidized polypeptide fails to bind either lysine vasopressin or oxytocin.