Abstract
The octacosapeptide sequence [Tyr 18] pro-ocytocin/neurophysin (1–18)NH 2 [ pro-OT Np(1–18)NH 2 ] was synthesized and used as substrate to detect endoprotease(s) possibly involved in the processing of this precursor in bovine hypothalamo-neurohypophyseal tract. An endopeptidase (58 Kda) was detected in lysates made from highly purified neurosecretory granules. This protease which cleaves the peptide bond on the carboxyl side of the Lys-Arg doublet, and no single basic residue, generates both OT-Gly 10-Lys 11-Arg 12+Ala 13-Val-Leu-Asp-Leu-Tyr 18(NH 2) from the octacosapeptide substrate. In addition, a carboxypeptidase B-like activity converting OT-Gly 10-Lys 11-Arg 12 into OT-Gly 10 was detected in the same granule lysates. It is hypothesized that a combination of these endoprotease and carboxypeptidase B-like activities together with the amidating enzyme of secretory granules might participate in the cleavage and processing of pro-OT Np in vivo .
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