Galactonolactone Dehydrogenase Requires a Redox-Sensitive Thiol for Optimal Production of Vitamin C1.

N.G.H. Leferink, E. van Duijn, A. Barendregt, A.J.R. Heck, W.J.H. van Berkel

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34 Citations (Scopus)


The mitochondrial flavoenzyme L-galactono--lactone dehydrogenase (GALDH) catalyzes the ultimate step of vitamin C biosynthesis in plants. We found that recombinant GALDH from Arabidopsis (Arabidopsis thaliana) is inactivated by hydrogen peroxide due to selective oxidation of cysteine (Cys)-340, located in the cap domain. Electrospray ionization mass spectrometry revealed that the partial reversible oxidative modification of Cys-340 involves the sequential formation of sulfenic, sulfinic, and sulfonic acid states. S-Glutathionylation of the sulfenic acid switches off GALDH activity and protects the enzyme against oxidative damage in vitro. C340A and C340S GALDH variants are insensitive toward thiol oxidation, but exhibit a poor affinity for L-galactono-1,4-lactone. Cys-340 is buried beneath the protein surface and its estimated pKa of 6.5 suggests the involvement of the thiolate anion in substrate recognition. The indispensability of a redox-sensitive thiol provides a rationale why GALDH was designed as a dehydrogenase and not, like related aldonolactone oxidoreductases, as an oxidase
Original languageEnglish
Pages (from-to)596-605
JournalPlant Physiology
Issue number2
Publication statusPublished - 2009


  • gamma-lactone dehydrogenase
  • ascorbic-acid
  • l-galactono-1,4-lactone dehydrogenase
  • glutathionyl-hemoglobin
  • arabidopsis-thaliana
  • sweet-potato
  • biosynthesis
  • purification
  • enzyme
  • expression


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