Enzymatic Degradation of Thyrotropin Releasing Hormone by Pancreatic Homogenates
作者:
Sonia Aratan-Spire,
Bryan Wolf,
Paul Czernichow,
期刊:
Neuroendocrinology
(Karger Available online 1986)
卷期:
Volume 42,
issue 5
页码: 399-406
ISSN:0028-3835
年代: 1986
DOI:10.1159/000124478
出版商: S. Karger AG
关键词: TRH;His-Pro diketopiperazine;Pancreas;Plasma;Diisopropylfluorophosphate;2-Jodoacetamide;Proglutamate aminopeptidase;Deamidase;TRH-specific degrading enzyme
数据来源: Karger
摘要:
Characteristics of pancreatic TRH-degrading activity were determined using [L-proline-2,3-3H] TRH and [L-histidine-2,5-3H] TRH as tracers and thin-layer chromatography to detect, identify and quantify TRH metabolites following incubation of tritiated TRH with pancreatic homogenates. The apparent Km of pancreatic enzymes was 2.2 10–5M, the V, 45 pmol/min, and the apparent specific activity, 62.3 ±3.45 pmol/min/mg total protein. In conditions of enzyme saturation, the percent of TRH degraded was found to be similar to the sum of degraded products formed (TRH-OH and His-Pro). Based on the chromatographic identification of metabolites, the presence of a deamidase pathway and a non-deamidase pathway in the TRH-degradation process of the pancreas was postulated. To better characterize the corresponding pancreatic enzymes, active site-directed inhibitors were then used and metabolites yielded were compared to those obtained in the same experimental conditions using plasma as enzyme source. The detection of His-Pro diketopiperazine among the metabolites was of especial interest since this biologically active metabolite was also found in the pancreas as an endogenous peptide and reported to be either a TRH degradation product or derived from sources other than just TRH. However, in presence of inhibitors, His-Pro diketopiperazine was only detected using plasma as enzyme source. Nevertheless, a pancreatic contribution to plasma TRH-degrading activity cannot be discard
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