Which molecule acts as an electron donor in bacterial oxidative stress response?
Redox homeostasis during oxidative stress requires continuous electron flow from reduced pyridine nucleotide NADPH generated by pentose phosphate pathway to thiol antioxidant enzymes. Thioredoxin is small 12 kDa dithiol protein with highly conserved WCGPC active motif forming reversible intramolecular disulfide acting as mobile electron shuttle. Reduced thioredoxin provides low-potential electrons directly to peroxiredoxins such as AhpC and Tpx that reduce hydrogen peroxide and organic peroxides to water and alcohols, to methionine sulfoxide reductases MsrA and MsrB that repair oxidized methionine residues in damaged proteins, and to ribonucleotide reductase converting ribonucleotides to deoxyribonucleotides for DNA synthesis. It also reduces OxyR disulfide when peroxide stress subsides and repairs aberrant disulfides formed in cytoplasmic proteins. Peroxiredoxin is acceptor not donor, peptidoglycan is envelope heteropolymer, DNA gyrase is topoisomerase modulating supercoiling, so thioredoxin uniquely functions as principal electron donor linking NADPH to diverse detoxification and biosynthetic reactions, explaining its essentiality and deep conservation across life.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 7: Thioredoxin as Electron Donor in Oxidative Defense.