Proteolytic conversion of neurohypophyseal peptides by rat thymocytes: involvement of endopeptidases.
The proteolytic conversion of oxytocin and Arg8-vasopressin by purified rat thymocytes was studied at 37 degrees C and physiological pH 7.4. The formed peptide fragments were isolated by high performance liquid chromatography and characterized by amino acid analysis. When oxytocin was incubated with rat thymocytes, oxytocin 1-8 and oxytocin 1-7 were isolated. In contrast, only Arg8-vasopressin 1-8 was found when Arg8-vasopressin was incubated with thymocytes. The formation of oxytocin 1-8, oxytocin 1-7 and Arg8-vasopressin 1-8 was prevented partially by 10(-3) M phenylmethylsulfonyl fluoride and iodoacetamide, and abolished by 0.5 x 10(-3) M Zn2+ and Hg2+ ions and 10(-3) M o-phenanthroline, but not by 10(-5) M leupeptin, lima bean trypsin inhibitor, trasylol, captopril and phosphoramidon. 0.5 x 10(-3) M EDTA was without effect on the formation of oxytocin 1-8 and Arg8-vasopressin 1-8 but increased by about 30% the formation of oxytocin 1-7. The results suggest that proteases capable of metabolizing oxytocin and Arg8-vasopressin are localized in the thymocyte surface membrane. Since oxytocin and vasopressin are synthetized by thymic epithelial cells and exert several actions on thymocytes, these proteases may play a physiological role in the inactivation of neurohypophyseal peptides at the thymocyte level.
Melis
M R
MR
Bernard B. Brodie Department of Neurosciences, University of Cagliari, Italy.
Stancampiano
R
R
Argiolas
A
A
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism*; D009479:Neuropeptides / Q000737:chemistry / Q000378:metabolism*; D010121:Oxytocin / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D051381:Rats; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism*
D000596:Amino Acids; D009479:Neuropeptides; D001127:Arginine Vasopressin; D010121:Oxytocin; D010450:Endopeptidases; D010447:Peptide Hydrolases