Redox regulation of homocysteine-dependent glutathione synthesis.
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, H(2)O(2) 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.
Vitvitsky
Victor
V
National Research Center for Hematology, Moscow, Russia.
Mosharov
Eugene
E
Tritt
Michael
M
Ataullakhanov
Fazoil
F
Banerjee
Ruma
R
D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D002460:Cell Line; D003541:Cystathionine beta-Synthase / Q000378:metabolism; D003542:Cystathionine gamma-Lyase / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D005981:Glutathione Synthase / Q000378:metabolism; D006710:Homocysteine / Q000737:chemistry*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007656:Ketoglutaric Acids / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D013482:Superoxide Dismutase / Q000378:metabolism; D013997:Time Factors; D014810:Vitamin E / Q000378:metabolism; D020122:tert-Butylhydroperoxide / Q000378:metabolism
D000975:Antioxidants; D007656:Ketoglutaric Acids; D006710:Homocysteine; D014810:Vitamin E; D020122:tert-Butylhydroperoxide; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase; D003541:Cystathionine beta-Synthase; D003542:Cystathionine gamma-Lyase; D005721:Glutamate-Cysteine Ligase; D005981:Glutathione Synthase; D005978:Glutathione; D003545:Cysteine; D001205:Ascorbic Acid