C-terminally extended ocytocin and pro-ocytocin: neurophysin peptide converting enzyme in bovine corpus luteum.

Purified secretory granules from the corpus luteum of super ovulated and fecundated cows, at day 7-8 after the heat period, were used as a source of pro-ocytocin/neurophysin (pro OT/Np) processing enzymes. An endoprotease comparable to the previously described pituitary enzyme both by its catalytic properties and sensitivity to various inhibitors was characterized. This protease cleaves pro OT/Np (1-20) after the basic Lys11Arg12 doublet to release OT Gly10 Lys11 Arg12. Moreover C-terminally extended ocytocin, i.e. OTGlyLys and OTGlyLysArg together with ocytocin were identified in extracts from the corpus luteum. Together these data argue strongly in favor of pro OT/Np processing pathways in which cleavage of the precursor at the Arg12-Ala13 peptide bond is the primary event.