Journal
REDOX REPORT
Volume 8, Issue 1, Pages 57-63Publisher
MANEY PUBLISHING
DOI: 10.1179/135100003125001260
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Funding
- NHLBI NIH HHS [HL58984] Funding Source: Medline
- NIEHS NIH HHS [ES011441] Funding Source: Medline
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [R01HL058984] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF ENVIRONMENTAL HEALTH SCIENCES [R03ES011441] Funding Source: NIH RePORTER
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In certain tissues, glutathione biosynthesis is connected to methionine metabolism via the trans-sulfuration pathway. The latter condenses homocysteine and serine to cystathionine in a reaction catalyzed by cystathionine beta-synthase followed by cleavage of cystathionine to cysteine and alpha-ketoglutarate by gamma-cystathionase. Cysteine is the limiting amino acid in glutathione biosynthesis, and studies in our laboratory have shown that approximately 50% of the cysteine in glutathione is derived from homocysteine in human liver cells. In this study, we have examined the effect of pro- and antioxidants on the flux of homocysteine through the trans-sulfuration pathway in the human hepatoma. cell line, HepG2. Our studies reveal that pyrrolidine dithiocarbamate and butylated hydroxyanisole enhance the flux of homocysteine through the trans-sulfuration pathway as has been observed previously with the pro-oxidants, H2O2 and tertiary butyl hydroperoxide. In contrast, antioxidants such as catalase, superoxide dismutase and a water-soluble derivative of vitamin E elicit the opposite effect and result in diminished flux of homocysteine through the trans-sulfuration pathway. These studies provide the first evidence for the reciprocal sensitivity of the trans-sulfuration pathway to pro- and antioxidants, and demonstrate that the upstream half of the glutathione biosynthetic pathway (i.e. leading to cysteine biosynthesis) is redox sensitive as is the regulation of the well-studied enzymes in the downstream half (leading from cysteine to glutathione), namely, gamma-glutamyl-cysteine ligase and glutathione synthetase.
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