Metabolism of L-cysteine in rats fed low and high protein diets.
L-Cysteine (5.0 mmol per kg of body weight) was intraperitoneally injected into rats fed a 25% casein or 5% casein diet. Concentrations of acidic and neutral amino acids in various tissues were determined 2 h later. In the rats fed the 25% casein diet there was a tendency for tissue amino acid and glutathione levels to be slightly lower than controls. In the 5% casein diet group, however, concentrations of tissue amino acids and glutathione generally increased after L-cysteine administration. S-(2-Hydroxy-2-carboxyethylthio)cysteine (HCETC,3-mercaptolactate-cysteine disulfide), though in trace amounts, was detected in kidney and blood plasma in the 5% casein diet group. Increases in cysteine-glutathione disulfide in liver, kidney and erythrocytes in the 5% casein diet group were considerable. These results indicate that L-cysteine was rapidly metabolized in the 25% casein diet group through the oxidative pathway, while in the 5% casein diet group, in which liver cysteine dioxygenase activity is supposed to be quite low, the oxidative metabolism of L-cysteine decreased and part of the L-cysteine was metabolized through the transaminative pathway. Administration of 15.0 mmol L-cysteine per kg of body weight to rats fed the 25% casein diet resulted in an increase in cysteine-glutathione disulfide in liver, kidney and erythrocytes, and the appearance of HCETC in blood plasma.(ABSTRACT TRUNCATED AT 250 WORDS)
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism*; D050558:Cysteine Dioxygenase; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D049308:Dioxygenases; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism; D008297:Male; D010105:Oxygenases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D000637:Transaminases / Q000378:metabolism
D000596:Amino Acids; D002364:Caseins; D004044:Dietary Proteins; C001705:beta-mercaptolactate cysteine disulfide; C031586:cysteine-glutathione disulfide; D010105:Oxygenases; D049308:Dioxygenases; D050558:Cysteine Dioxygenase; D000637:Transaminases; D005978:Glutathione; D003545:Cysteine