Enzyme kinetic studies and inhibition by oligopeptides of LH-RH degradation in rat hypothalamus and pituitary

Neuroendocrinology
H KuhlH D Taubert

Abstract

The enzyme kinetic parameters of the degradation of luteinizing hormone-releasing hormone (LH-RH) and L-cystine-bis-(4-nitroanilide) (Cys-NA) by rat hypothalamic (HYP) and pituitary (PIT) extracts and the effect of various oligopeptides on the rate of LH-RH inactivation were investigated in vitro. The 105,000 x g supernatant of 1 rat HYP inactivated 57 microgram LH-RH during a 30 min incubation (Km = 12.4 microM, V max = 2.33 microgram LH-RH/mg protein/min), and of one rat anterior PIT, 48 microgram LH-RH during 30 min of incubation (Km = 12.2 microM, V max = 8.0 microgram LH-RH/mg protein/min). The synthetic substrate Cys-NA competitively inhibited LH-RH degradation with a Ki of 8.5 microM in the HYP and 6 microM in the PIT enzyme preparation. Vice versa, LH-RH also competitively inhibited the cleavage of Cys-NA with inhibition constants of 14 microM (HYP) and 15 microM (PIT) indicating that the 2 substrates are probably cleaved by the same enzyme. The most effective inhibitors of LH-RH degradation were found to be angiotensin-related peptides, neurotensin, bradykinin, and bacitracin. A relatively weak effect was obtained with oxytocin, enkephalin and puromycin. It is concluded that endogenous oligopeptides such as angiotensin...Continue Reading

Citations

Jan 1, 1980·Peptides·W K SamsonS M McCann
Nov 1, 1983·Molecular and Cellular Endocrinology·E C Griffiths, J R McDermott
Nov 7, 2002·Toxicon : Official Journal of the International Society on Toxinology·Elaine Gasparello-Clemente, Paulo Flávio Silveira
Feb 1, 1985·Proceedings of the National Academy of Sciences of the United States of America·R A Skidgel, E G Erdös
Oct 31, 1980·Biochemical and Biophysical Research Communications·P LeblancC Kordon

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