CHARACTERISTICS OF PLASMA TRH-DEGRADING ENZYME

Google Scholar
  • 1 January 1975
    • journal article
    • research article
    • Vol. 19  (3) , 277-287
Abstract
The reaction products of plasma enzyme degradation of TRH (thyrotropin releasing hormone) were identified by TLC. The enzyme in normal rat plasma yields proline and pGlu-His as major reaction products. High concentrations of proline decrease peptide cleavage, resulting in greater amounts of acid TRH. The apparent Km of the enzyme is 4.1 .times. 10-6M. Luteinizing hormone releasing hormone and neurotensin are competitive inhibitors with Ki of 5 .times. 10-6M and 1.5 .times. 10-5M, respectively. Somatostatin, melanocyte stimulating hormone inhibitory factor, oxytocin, arg-vasopressin, arg-vasotocin, neurophysin II and glucagon do not compete; and pGlu-His-Pro-OH, Glu-His-Pro-OH, pGlu-His, His-Pro-NH2, and Pro-NH2 do not affect enzyme activity. The substrate may require pGlu and a terminal or internal amide to complex with the enzyme. The enzyme is markedly inhibited by Cu++, benzamadine, p-(chloromercuri)-benzoic acid, moderately affected by EDTA and puromycin, and unaffected by mercaptoethanol. TSH does not affect enzyme activity while luteinizing hormone inhibits it moderately at high concentrations (300-600 pg/ml).

This publication has 1 reference indexed in Scilit: