Differential regulation of glutamate-cysteine ligase subunit expression and increased holoenzyme formation in response to cysteine deprivation

Jeong In Lee, Joann Kang, Martha H. Stipanuk

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40 Scopus citations


GCL (glutamate-cysteine ligase) is a heterodimer of a GCLC (GCL catalytic subunit) that possesses all of the enzymatic activity and a GCLM (GCL modifier subunit) that alters the Ki of GCLC for GSH. We hypothesized that the expression of GCLM and the association of GCLM with GCLC were responsible for the apparent increase in GCL activity state observed in the liver of rats fed low-protein diets or in hepatocytes cultured in low-sulphur amino acid-containing medium. Therefore we conducted a series of studies using rats and a human hepatoma (HepG2/C3A) cell line to assess the role of GCLM and holoenzyme formation in the regulation of GCL activity in response to sulphur amino acid intake or availability. Increases in GCL activity in rat liver, as well as in HepG2 cells, were due to the additive effects of changes in the amount of GCLC and the kcat for GCLC. The increase in the k cat for GCLC was associated with increased holoenzyme formation, which was associated with an increase in the molar ratio of GCLM to GCLC. Furthermore, our results indicate that the GCLM level in rat liver is always limiting and that up-regulation of the GCLM level results in increased holoenzyme formation and an increase in the kcat. This is the first report demonstrating that the catalytic efficiency of rat GCL is increased by holoenzyme formation and the first demonstration of differential up-regulation of the GCL subunits in response to cysteine deprivation.

Original languageEnglish (US)
Pages (from-to)181-190
Number of pages10
JournalBiochemical Journal
Issue number1
StatePublished - Jan 1 2006



  • Cysteine
  • Glutamate-cysteine ligase (GCL)
  • Glutathione (GSH)
  • HepG2/C3A cells
  • Holoenzyme
  • Low-protein diet

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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