Evolution of Neurophysin Proteins: The I Sequence of Bovine Neurophysin-I (vasopressin/oxytocin/carrier proteins/automated amine

The sequence of the first 50 amino-acid residues of bovine neurophysin-I was determined. A com- parison of this sequence with that of the 97-residue bovine neurophysin-II and the 92-residue porcine neurophysin-I molecules reveals a high degree of homology among these proteins. It is suggested that the binding site of neurophy- sin proteins for neurohypophyseal hormones is located in the middle portion of these molecules, where their se- quences are virtually identical. The sequence data, as well as the occurrence of at least two neurophysins in both the pig and the cow, suggest that; each species inherited at least two structural genes controlling the synthesis of these pro- teins. The most striking finding in the study was the ob- servation of internal sequence homologies within the neurophysins. This result implies that these molecules arose by way of a series of partial gene duplications of a primitive gene that coded for a smaller ancestral protein.