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)