ExplorEnz: EC 1.3.2.3

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1.3.2.3

Accepted name:

L-galactonolactone dehydrogenase

Reaction:

L-galactono-1,4-lactone + 4 ferricytochrome c = L-dehydroascorbate + 4 ferrocytochrome c + 4 H⁺ (overall reaction)
(1a) L-galactono-1,4-lactone + 2 ferricytochrome c = L-ascorbate + 2 ferrocytochrome c + 2 H⁺
(1b) L-ascorbate + 2 ferricytochrome c = L-dehydroascorbate + 2 ferrocytochrome c + 2 H⁺ (spontaneous)

Other name(s):

galactonolactone dehydrogenase; L-galactono-γ-lactone dehydrogenase; L-galactono-γ-lactone:ferricytochrome-c oxidoreductase; GLDHase; GLDase

Systematic name:

L-galactono-1,4-lactone:ferricytochrome-c oxidoreductase

Comments:

This enzyme catalyses the final step in the biosynthesis of L-ascorbic acid in higher plants and in nearly all higher animals with the exception of primates and some birds [5]. The enzyme is very specific for its substrate L-galactono-1,4-lactone as D-galactono-γ-lactone, D-gulono-γ-lactone, L-gulono-γ-lactone, D-erythronic-γ-lactone, D-xylonic-γ-lactone, L-mannono-γ-lactone, D-galactonate, D-glucuronate and D-gluconate are not substrates [5]. FAD, NAD⁺, NADP⁺ and O₂ (cf. EC 1.3.3.12, L-galactonolactone oxidase) cannot act as electron acceptor [5].

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9029-02-1

References:

1.	Mapson, L.W. and Breslow, E. Properties of partially purified L-galactono-γ-lactone dehydrogenase. Biochem. J. 65 (1957) 29.
2.	Mapson, L.W., Isherwood, F.A. and Chen, Y.T. Biological synthesis of L-ascorbic acid: the conversion of L-galactono-γ-lactone into L-ascorbic acid by plant mitochondria. Biochem. J. 56 (1954) 21–28. [PMID: 13126087]
3.	Isherwood, F.A., Chen, Y.T. and Mapson, L.W. Synthesis of L-ascorbic acid in plants and animals. Biochem. J. 56 (1954) 1–15. [PMID: 13126085]
4.	Ôba, K., Ishikawa, S., Nishikawa, M., Mizuno, H. and Yamamoto, T. Purification and properties of L-galactono-γ-lactone dehydrogenase, a key enzyme for ascorbic acid biosynthesis, from sweet potato roots. J. Biochem. (Tokyo) 117 (1995) 120–124. [PMID: 7775377]
5.	Østergaard, J., Persiau, G., Davey, M.W., Bauw, G. and Van Montagu, M. Isolation of a cDNA coding for L-galactono-γ-lactone dehydrogenase, an enzyme involved in the biosynthesis of ascorbic acid in plants. Purification, characterization, cDNA cloning, and expression in yeast. J. Biol. Chem. 272 (1997) 30009–30016. [DOI] [PMID: 9374475]

[EC 1.3.2.3 created 1961, modified 2006]