Evidence for distinct dibasic processing endopeptidases with Lys-Arg and Arg-Arg specificities in neurohypophysial secretory granules.
Two Ca(2+)-dependent endopeptidases endowed with specificities for paired basic residues have been disclosed in rat and ox neurohypophysial secretory granules. Specificities investigated by using synthetic fluorogenic substrates showed the presence of a Lys-Arg endopeptidase with optimum pH close to the granule pH (5.5) and of an Arg-Arg endopeptidase more active at pH 7.0. Granule extracts have virtually no activity towards Lys-Lys-containing substrate or monobasic substrates. Pro-Gly-Lys-Arg-chloromethylketone appears a very efficient inhibitor for the Lys-Arg enzyme. Soluble and membrane-bound forms of both endopeptidases have been detected. pH-dependence of membrane binding and partitioning into Triton X-114 suggest that the membrane-bound form of Lys-Arg endopeptidase is associated through an amphiphilic alpha-helix. It is proposed that the enzyme Lys-Arg cleaves prooxytocin and provasopressin at their signal sequence Gly-Lys-Arg when these precursors arrive in the neurosecretory granules. The processing proceeds in the granules through carboxypeptidase E and alpha-amidating enzyme complex for giving mature pharmacologically active nonapeptide hormones.
Rouille
Y
Y
Laboratory of Biological Chemistry, University of Paris VI, France.
Spang
A
A
Chauvet
J
J
Acher
R
R
D000818:Animals; D001127:Arginine Vasopressin; D002417:Cattle; D003594:Cytoplasmic Granules / Q000201:enzymology*; D010450:Endopeptidases / Q000378:metabolism*; D009481:Neurophysins; D010121:Oxytocin / Q000031:analogs & derivatives / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000201:enzymology*; D011480:Protease Inhibitors; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D014667:Vasopressins / Q000378:metabolism
D009481:Neurophysins; D010455:Peptides; D011480:Protease Inhibitors; D011498:Protein Precursors; D014667:Vasopressins; D001127:Arginine Vasopressin; D010121:Oxytocin; C046278:oxytocin, Gly-Lys-Arg-; D010450:Endopeptidases