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Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853
To determine the role of nonsulfur vs. sulfur
amino acids in regulation of cysteine metabolism, rats were fed a basal
diet or diets supplemented with a mixture of nonsulfur amino acids (AA), sulfur amino acids (SAA), or both for 3 wk. Hepatic
cysteine-sulfinate decarboxylase (CSDC), cysteine dioxygenase (CDO),
and
-glutamylcysteine synthetase (GCS) activity, concentration, and
mRNA abundance were measured. Supplementation with AA alone had no
effect on any of these measures. Supplementation of the basal diet with
SAA, with or without AA, resulted in a higher CDO concentration
(32-45 times basal), a lower CSDC mRNA level (49-64% of
basal), and a lower GCS-heavy subunit mRNA level (70-76%). The
presence of excess SAA and AA together resulted in an additional type
of regulation: a lower specific activity of all three enzymes was
observed in rats fed diets with an excess of AA and SAA. Both SAA and
AA played a role in regulation of these three enzymes of cysteine
metabolism, but SAA had the dominant effects, and effects of AA were
not observed in the absence of SAA.
cysteine-sulfinate decarboxylase; cysteine dioxygenase;
-glutamylcysteine synthetase; sulfate; taurine
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