Neurophysins and posterior pituitary hormones in the Suiformes

Abstract

The neurophysins are proteins that bind the posterior pituitary hormones within the neurosecretory vesicles of the vertebrate neurohypophysis. In the pig, immunofluorescence localization of porcine neurophysin II suggests that this protein is stored with [8-lysine]-vasopressin (LVP). Gel electrophoresis and immunodiffusion of neurohypophysial proteins from two other Suiformes species, the hippopotamus and warthog, hitherto thought to contain LVP, reveal that the warthog has a protein electrophoretically and immunologically identical with porcine neurophysin II, whereas the neurohypophysial proteins of the hippopotamus do not cross-react with a rabbit antiserum specific to this protein. The vasopressins of the hippopotamus and warthog have been recharacterized by gel filtration and by thinlayer chromatography in two solvent systems not hitherto used for this purpose. The presence of LVP in the warthog has been confirmed, but only [8-arginine]-vasopressin (AVP) was detected in the hippopotamus. This suggests that the hippopotamus possesses only AVP, or that the occurrence of LVP in this species is sufficiently rare to make it undetectable by the above techniques. The two species of the Family Suidae studied, i. e. the pig and the warthog, thus seem to be closely related to the structure of their vasopressins and neurophysins, whereas the hippopotamus (Family Hippopotamidae) is less closely related, and seems in this respect to be more similar to other Artiodactyls. This contrasts with the earlier identification of the hippopotamus vasopressin as LVP, which gave biochemical support for the inclusion of the Hippopotamidae within the Suiformes. The weight of the biochemical evidence now favours a contrary view.