The Neurohypophysial Hormone‐Binding Proteins: Complete Amino‐Acid Sequence of Ovine and Bovine MSEL‐Neurophysins

Abstract

Ovine and bovine MSEL‐neurophysins, purified by hormone protein complex precipitation, molecular sieving and ion‐exchange chromatography, were subjected either to performic acid oxidation or to reduction and carboxamidomethylation. Cleavage by trypsin gave in each case eight fragments which were separated by peptide mapping. They were sequenced either directly by Edman degradation or after sub‐cleavage by subtilisin, chymotrypsin, thermolysin, pepsin or partial acid hydrolysis and characterization of the sub‐peptides.Alignment of the tryptic fragments was determined by automated Edman degradation and by identification of overlapping peptides obtained after hydrolysis of the polypeptide chain by chymotrypsin, pepsin and subtilisin. Bovine tryptic peptides were arranged, in part, according to their homology with ovine peptides.Both ovine and bovine MSEL‐neurophysins comprise 95 residues; in both cases, a three‐residue N‐terminal truncated form can be detected. Ovine and bovine MSEL‐neurophysins are nearly identical. Two positions are different: 48 (isoleucine in ovine and asparagine in bovine) and 89 which shows a microheterogeneity in the ox (isoleucine in ovine. isoleucine or valine in bovine). Porcine MSEL‐neurophysin presents four differences when compared with ovine homologue (positions 48, 89, 90 and 92) and an apparent three‐residue C‐terminal deletion.MSEL‐neurophysins form a protein family which appears to be evolutionary stable in species of Artiodactyla. In this order of mammals, the rare variations seem to occur in the C‐terminal sequence. A second family of related neurophysins found in mammals. VLDV‐neurophysins, shows substitutions in the N‐terminal sequence when compared to MSEL‐neurophysins. There is a large invariant central part in the polypeptide chain which might include the neurophysial hormone‐binding domain of all neurophysins.