Identification and metabolic differentiation of rat neurophysins: a microelectrophoretic study

Proteins of the hypothalamo-neurohypophysial system of the rat were studied by means of a purpose-modified form of microelectrophoresis in the polyacrylamide gradient. The respective shares of neurophysins I, II and III in total neurophysin were found to be 58 +/- 16, 24 +/- 5 and 18 +/- 6% in HCl extracts and 48 +/- 7, 30 +/- 7 and 23 +/- 5% in aqueous extracts. In particular, neurophysin I was absent in homozygous Brattleboro rats, with no evidence being obtained as to aberrant neurophysins. Approximately equal neurophysin shares were observed for heterozygous Brattleboro rats. Using perfused material, one of the fractions occurring in neurohypophysial extracts was clearly identified as serum albumin. The electropherograms of aqueous neurohypophysial extracts revealed up to 43 protein fractions. Comparison with extracts from the median eminence, the nuclei of the hypothalamo-neurohyophysial system and other hypothalamic regions, as well as the results of incubation experiments distinguished one fraction as a possible candidate for the hitherto hypothetical neurophysin precursors. Incubation of neurohypophyses did not yield any signs of both conversion of neurophysin II into neurophysin III, and formation of further neurophysin derivatives.