title: Down-regulation of rat liver beta-adrenergic receptors by cysteine.
abstract: Down-regulation of hepatic beta-adrenergic receptors was indicated by a 56% decrease in the specific activity of 125I-iodocyanopindolol bound to rat liver membrane preparations from rats fed diets containing 15% of casein supplemented with cysteine, instead of methionine or unsupplemented. Down-regulation of hepatic beta-adrenergic receptors by cysteine appears to be mediated through an effect of cysteine on the tissue concentration of S-adenosyl methionine (SAM). The liver tissue concentration of SAM in rats fed cysteine-supplemented diets decreased 53% compared to those fed diets supplemented with methionine. The decrease in liver SAM in rats fed the diet supplemented with cysteine appears to reflect a non-competitive inhibition of methionine adenosyl-transferase by cysteine. Lineweaver-Burk plots demonstrated a dose-related Vmax response to cysteine but did not change the apparent Km at any concentration tested.
mesh_terms: D000818:Animals; D003545:Cysteine / Q000008:administration & dosage / Q000494:pharmacology*; D004032:Diet; D008099:Liver / Q000378:metabolism*; D008715:Methionine / Q000008:administration & dosage / Q000494:pharmacology; D008716:Methionine Adenosyltransferase / Q000037:antagonists & inhibitors; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism*
chemical_list: D011943:Receptors, Adrenergic, beta; D012436:S-Adenosylmethionine; D008715:Methionine; D008716:Methionine Adenosyltransferase; D003545:Cysteine