NADH-dependent dehydroascorbate reductase in the rabbit lens

The present investigation demonstrates the existence of NADH-dependent dehydroascorbate (DHA) reductase activity in the soluble fraction of the rabbit lens. This DHA reductase was specific for NADH, and its apparent Km values for DHA and NADH were 5.7 mM and 4.0 microM, respectively. In a gel filtration of the lens soluble fraction on a Sephadex G-75 superfine column, the NADH-dependent DHA reductase activity was eluted at the oligomeric betaL1-crystallin fraction, which may also contain lambda-crystallin (a rabbit-specific crystallin). Furthermore, about 80% of protein fractions separated from the betaL1-crystallin fraction by DEAE-cellulose ion-exchange column chromatography exhibited DHA reductase activity. In the SDS-PAGE analysis of the protein fractions with DHA reductase activity, 32-33, 27 and 25 kDa protein subunits were commonly identified. These results suggest that oligomers of beta-crystallin and/or lambda-crystallin subunits may be associated with the DHA reductase activity. The present paper also discusses that the function of the reductase may be to enhance the antiphotoxidation capacity of the lens.