RATS FED A LOW-PROTEIN DIET SUPPLEMENTED WITH SULFUR AMINO-ACIDS HAVEINCREASED CYSTEINE DIOXYGENASE ACTIVITY AND INCREASED TAURINE PRODUCTION IN HEPATOCYTES
Pj. Bagley et Mh. Stipanuk, RATS FED A LOW-PROTEIN DIET SUPPLEMENTED WITH SULFUR AMINO-ACIDS HAVEINCREASED CYSTEINE DIOXYGENASE ACTIVITY AND INCREASED TAURINE PRODUCTION IN HEPATOCYTES, The Journal of nutrition, 125(4), 1995, pp. 933-940
The metabolism of cysteine and cysteinesulfinate and the activities of
key enzymes in cysteine catabolic pathways were investigated in hepat
ocytes isolated from rats fed a basal (100 g casein/kg) diet or the di
et supplemented with L-methionine (3 or 10 g/kg diet) or the sulfur eq
uivalent as L-cystine (2.4 or 8 g/kg diet). Cysteine dioxygenase activ
ity was higher in hepatocytes from rats fed diets with the higher leve
l of sulfur amino acid supplementation, and the higher enzyme activity
was paralleled by a greater total catabolite production (taurine + su
lfate) from cysteine. Taurine production as a percentage of total cyst
eine catabolism was significantly greater in hepatocytes from rats fed
the diet with excess methionine or cystine (basal, 22%; excess methio
nine, 61%, excess cystine, 49%). Glutathione production was markedly l
ower in hepatocytes from rats fed excess sulfur amino acids such that
total cysteine utilization was similar for all dietary treatments. Cys
teinesulfinate decarboxylase activity and catabolism of cysteinesulfin
ate by hepatocytes were unaffected by the dietary supplementations. Re
sults are in contrast to previous studies in which increased dietary p
rotein resulted in decreased cysteinesulfinate decarboxylase activity
and decreased partitioning of cysteinesulfinate to taurine vs. sulfate
. Thus, sulfur amino acids may be less effective than protein in decre
asing cysteinesulfinate decarboxylase activity and may result in a pat
tern of sulfur catabolite production from cysteine that favors taurine
production.