Recombinant thioredoxin h (Trx h2) overproduced in E. coli (M15) was purified by Ni2+- chelate affinity chromatography as previously reported (Huang et al., 2004a). The molecular mass of Trx h2 was ca. 14 kDa determined by SDS (sodium dodecyl sulfate)-PAGE (polyacrylamide gel electrophoresis). It had antioxidant activity (Huang et al., 2004b) and it reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate ascorbate (AsA). However, without glutathione, Trx h2 had very low DHA reductase activity. AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radicals. MDA was also reduced by Trx h2 to AsA in the presence of NADH mimicking the MDA reductase catalyzed reaction. These data suggest that Trx h2 has both DHA reductase and MDA reductase activities.
