The molecular aspects and physiological significance of NADP(+)-dependent D-arabinose dehydrogenase (ARA), which is thought to function in the biosynthesis of an analog of ascorbic acid, D-erythroascorbic acid in yeasts, were examined. A large subunit of ARA, Ara1p produced in E. coli, was purified as a homodimer, some of which was degraded at the N-terminus. It showed sufficient ARA activity. Degradation of Ara1p occurs naturally in yeast cells, and the small subunit of ARA previously thought as is, in fact, a naturally occuring degradation product of Ara1p. A deficient mutant of ARA1 lost almost all NADP(+)-ARA activity, but intracellular D-erythroascorbic acid was only halved. This mutant showed increased susceptibility to H(2)O(2) and diamide but not to menadione or tert-butylhydroperoxide. Feeding D-arabinose to mutant cells led to increases in intracellular D-erythroascorbic acid, suggesting the presence of another ARA isozyme. The deficient mutant of ARA1 recovered resistance to H(2)O(2) with feeding of D-arabinose. Our results suggest that the direct contributions of Ara1p both to D-erythroascorbic acid biosynthesis and to oxidative stress resistance are quite limited.

• PMID: 17151466
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Amako K, Fujita K, Iwamoto C, Sengee M, Fuchigami K, Fukumoto J, Ogishi Y, Kishimoto R, Goda K

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