Purification and Properties of L-Galactono- γ-Lactone Dehydrogenase, a Key Enzyme for Ascorbic Acid Biosynthesis, from Sweet Potato Roots
- 1 January 1995
- journal article
- research article
- Published by Oxford University Press (OUP) in The Journal of Biochemistry
- Vol. 117 (1) , 120-124
- https://doi.org/10.1093/oxfordjournals.jbchem.a124697
Abstract
L-Galactono-γ-lactone dehydrogenase (L-galactono-γ-lactone:ferricytochrome c oxidore-ductase [EC 1.3.2.3], GLDHase) which catalyzes the terminal step in the biosynthesis of L-ascorbic acid (AsA) has been purified from roots of sweet potato (Ipomoea batatas L., cv. Kintoki). Highly purified preparation of the GLDHase was obtained by three column chromatography steps with a recovery of ca. 1%, after solubilization from mitochondria in sweet potato roots. SDS-PAGE exhibited a single band at 56 kDa. In the native state, the apparent molecular mass of the enzyme was 56 kDa, based on a Sephadex G-100 gel filtration. The pi and optimum pH values were 5.8 and 7.9, respectively. The Km value for L-galactono-γ-lactone was 0.12 mM. Substrate inhibition was obtained at concentrations greater than 4.2 mM. The enzyme was inhibited by p-chloromercuribenzoate (PCMB) and acriflavine, and the inhibition of acriflavine was diminished by the addition of FAD or FMN. The only effective substrate for the GLDHase was L-galactono-γ-lactone.Keywords
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