Figure 1.

Redox cycling regenerates antioxidants and requires GSH. Antioxidants undergo multiple rounds of reduction–oxidation at active site cysteine residues, which are represented by the disulfide (S-S) and SH, respectively. GSH provides the reducing equivalents for these reactions involving the reduction in harmful hydrogen peroxide and organic peroxides (ROOH) by GPx or neutralization of reactive aldehydes, such as HNE, through addition of GSH by GST. GSSG is replenished to GSH by either NADP-dependent GR or Grx. NADPH is produced by reaction with glucose 6-phosphate dehydrogenase. NADPH, nicotinamide adenine dinucleotide phosphate; GSH, reduced glutathione; GSSR, oxidized glutathione; GR, glutathione reductase; GPx, glutathione peroxidase; Grx, glutaredoxin; GST, glutathione S-transferase; G6-PDH, glucose 6-phosphate dehydrogenase.