Redox regulation of homocysteine-dependent glutathione synthesis

Redox Rep. 2003;8(1):57-63. doi: 10.1179/135100003125001260.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antioxidants / pharmacology
  • Ascorbic Acid / metabolism
  • Catalase / metabolism
  • Cell Line
  • Cystathionine beta-Synthase / metabolism
  • Cystathionine gamma-Lyase / metabolism
  • Cysteine / metabolism
  • Glutamate-Cysteine Ligase / metabolism
  • Glutathione / metabolism*
  • Glutathione Synthase / metabolism
  • Homocysteine / chemistry*
  • Humans
  • Hydrogen Peroxide / pharmacology
  • Ketoglutaric Acids / metabolism
  • Kinetics
  • Oxidation-Reduction*
  • Superoxide Dismutase / metabolism
  • Time Factors
  • Vitamin E / metabolism
  • tert-Butylhydroperoxide / metabolism


  • Antioxidants
  • Ketoglutaric Acids
  • Homocysteine
  • Vitamin E
  • tert-Butylhydroperoxide
  • Hydrogen Peroxide
  • Catalase
  • Superoxide Dismutase
  • Cystathionine beta-Synthase
  • Cystathionine gamma-Lyase
  • Glutamate-Cysteine Ligase
  • Glutathione Synthase
  • Glutathione
  • Cysteine
  • Ascorbic Acid