PURIFICATION AND CHARACTERIZATION OF DEHYDROASCORBATE REDUCTASE FROM RICE

Dehydroascorbate reductase (DHAR; EC 1.8.5.1) is an enzyme that is cri tical for maintenance of an appropriate level of ascorbate in plant ce lls. 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, b ut it was different from them in terms of heat stability and antigenic ity. The aminoterminal amino acid sequence of the DHAR from rice did n ot show any obvious similarity to those of known proteins with DHAR ac tivity, such as, glutaredoxin (thioltransferase), protein disulfide is omerase, and trypsin inhibitor. Immunoprecipitation analysis showed th at this enzyme was a major DHAR in etiolated seedlings. Western blot a nalysis indicated that this enzyme was distributed ubiquitously in ric e tissues. A similar protein was found in barley but not in dicots.