PMID- 18190525
OWN - NLM
STAT- MEDLINE
DCOM- 20080617
LR  - 20131121
IS  - 1742-464X (Print)
IS  - 1742-464X (Linking)
VI  - 275
IP  - 4
DP  - 2008 Feb
TI  - l-Galactono-gamma-lactone dehydrogenase from Arabidopsis thaliana, a flavoprotein 
      involved in vitamin C biosynthesis.
PG  - 713-26
LID - 10.1111/j.1742-4658.2007.06233.x [doi]
AB  - l-Galactono-1,4-lactone dehydrogenase (GALDH; ferricytochrome c oxidoreductase; 
      EC 1.3.2.3) is a mitochondrial flavoenzyme that catalyzes the final step in the 
      biosynthesis of vitamin C (l-ascorbic acid) in plants. In the present study, we 
      report on the biochemical properties of recombinant Arabidopsis thaliana GALDH 
      (AtGALDH). AtGALDH oxidizes, in addition to l-galactono-1,4-lactone (K(m) = 0.17 
      mm, k(cat) = 134 s(-1)), l-gulono-1,4-lactone (K(m) = 13.1 mm, k(cat) = 4.0 
      s(-1)) using cytochrome c as an electron acceptor. Aerobic reduction of AtGALDH 
      with the lactone substrate generates the flavin hydroquinone. The two-electron 
      reduced enzyme reacts poorly with molecular oxygen (k(ox) = 6 x 10(2) 
      m(-1).s(-1)). Unlike most flavoprotein dehydrogenases, AtGALDH forms a flavin N5 
      sulfite adduct. Anaerobic photoreduction involves the transient stabilization of 
      the anionic flavin semiquinone. Most aldonolactone oxidoreductases contain a 
      histidyl-FAD as a covalently bound prosthetic group. AtGALDH lacks the histidine 
      involved in covalent FAD binding, but contains a leucine instead (Leu56). Leu56 
      replacements did not result in covalent flavinylation but revealed the importance 
      of Leu56 for both FAD-binding and catalysis. The Leu56 variants showed remarkable 
      differences in Michaelis constants for both l-galactono-1,4-lactone and 
      l-gulono-1,4-lactone and released their FAD cofactor more easily than wild-type 
      AtGALDH. The present study provides the first biochemical characterization of 
      AtGALDH and some active site variants. The role of GALDH and the possible 
      involvement of other aldonolactone oxidoreductases in the biosynthesis of vitamin 
      C in A. thaliana are also discussed.
FAU - Leferink, Nicole G H
AU  - Leferink NG
AD  - Laboratory of Biochemistry, Wageningen University, The Netherlands.
FAU - van den Berg, Willy A M
AU  - van den Berg WA
FAU - van Berkel, Willem J H
AU  - van Berkel WJ
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20080110
PL  - England
TA  - FEBS J
JT  - The FEBS journal
JID - 101229646
RN  - 0 (Arabidopsis Proteins)
RN  - 0 (Flavoproteins)
RN  - 0 (Lactones)
RN  - EC 1.3.- (Oxidoreductases Acting on CH-CH Group Donors)
RN  - EC 1.3.2.3 (galactonolactone dehydrogenase)
RN  - PQ6CK8PD0R (Ascorbic Acid)
SB  - IM
MH  - Amino Acid Sequence
MH  - Arabidopsis/*enzymology/genetics
MH  - Arabidopsis Proteins/chemistry/genetics/*metabolism
MH  - Ascorbic Acid/*biosynthesis
MH  - Catalysis
MH  - Electrophoresis, Polyacrylamide Gel
MH  - Flavoproteins/chemistry/genetics/*metabolism
MH  - Lactones/metabolism
MH  - Models, Biological
MH  - Molecular Sequence Data
MH  - Mutagenesis, Site-Directed
MH  - Mutation
MH  - Oxidation-Reduction
MH  - Oxidoreductases Acting on CH-CH Group Donors/chemistry/genetics/*metabolism
MH  - Sequence Homology, Amino Acid
EDAT- 2008/01/15 09:00
MHDA- 2008/06/18 09:00
CRDT- 2008/01/15 09:00
PHST- 2008/01/15 09:00 [pubmed]
PHST- 2008/06/18 09:00 [medline]
PHST- 2008/01/15 09:00 [entrez]
AID - EJB6233 [pii]
AID - 10.1111/j.1742-4658.2007.06233.x [doi]
PST - ppublish
SO  - FEBS J. 2008 Feb;275(4):713-26. doi: 10.1111/j.1742-4658.2007.06233.x. Epub 2008 
      Jan 10.