NADP⁺-Dependent D-Arabinose Dehydrogenase Shows a Limited Contribution to Erythroascorbic Acid Biosynthesis and Oxidative Stress Resistance in Saccharomyces cerevisiae

Abstract

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 H₂O₂ 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 H₂O₂ 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.