Purification and characterization of dehydroascorbate reductase from rice

Dehydroascorbate reductase (DHAR; EC 1.8.5.1) is an enzyme that is critical for maintenance of an appropriate level of ascorbate in plant cells. This report describes the purification and characterization of a GSH-dependent DHAR from rice (Oryza sativa) bran and is the first, to our knowledge, of such an analysis of DHAR from a monocot. The enzyme was a monomeric thiol enzyme, resembling DHARs purified from dicots, but it was different from them in terms of heat stability and antigenicity. The aminoterminal amino acid sequence of the DHAR from rice did not show any obvious similarity to those of known proteins with DHAR activity, such as, glutaredoxin (thioltransferase), protein disulfide isomerase, and trypsin inhibitor. Immunoprecipitation analysis showed that this enzyme was a major DHAR in etiolated seedlings. Western blot analysis indicated that this enzyme was distributed ubiquitously in rice tissues. A similar protein was found in barley but not in dicots.