Effect of methionine-loading on methyl group synthesis and activation in rat brain and liver.
Much greater increases in S-adenosylmethionine concentrations are observed in the liver in response to methionine-loading than in the brain due to differences in the methionine adenosyltransferase activities in these tissues. Liver methione adenosyltransferase exhibits a bimodal saturation curve with a nonlinear Line-weaver-Burk plot, indicating that high methionine concentrations are required for saturation. In the brain the methionine adenosyltransferase is saturated in vitro at a methionine concentration less than the normal physiological concentration. The increased S-adenosylmethionine concentrations in the livers of methionine-treated rats also account for the observed inhibition of N5,N10-methylenetetrahydrofolate reductase activity in this tissue. No inhibition of this enzyme is observed in the brain of methionine treated animals. Nor are S-adenosylmethionine concentrations increased significantly in brain. Serine hydroxymethyltransferase activity responds to methionine-loading by decreasing in brain and increasing in liver.
D000818:Animals; D001921:Brain / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D012696:Glycine Hydroxymethyltransferase / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008297:Male; D008715:Methionine / Q000378:metabolism* / Q000494:pharmacology*; D008716:Methionine Adenosyltransferase / Q000378:metabolism; D008745:Methylation; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP) / Q000378:metabolism; D008780:Methyltransferases / Q000378:metabolism; D051381:Rats; D012436:S-Adenosylmethionine / Q000378:metabolism
D012436:S-Adenosylmethionine; D008715:Methionine; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP); D008780:Methyltransferases; D012696:Glycine Hydroxymethyltransferase; D008716:Methionine Adenosyltransferase