Dioscorins, the major tuber storage proteins of yam ( Dioscorea batatas Decne), with dehydroascorbate reductase and monodehydroascorbate reductase activities

Abstract

Dioscorins, the major storage proteins of yam ( Dioscorea batatas Decne), were purified from the tubers according to the methods of Hou et al. (W.C. Hou, J.S. Liu, H.J. Chen, T.E. Chen, C.F. Chang, Y.H. Lin, Dioscorin, the major tuber storage protein of yam ( Dioscorea batatas Decne), with carbonic anhydrase and trypsin inhibitor activities, J. Agric. Food Chem. 47 (1999) 2168–2172.). Dioscorins reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate ascorbate (AsA). However, without glutathione, dioscorins has very low DHA reductase activity. Intermolecular thiol–disulfide interchanges of dioscorins on SDS–PAGE gels were found during DHA reduction in the absence of glutathione. AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radicals. MDA was also reduced by dioscorins to AsA in the presence of NADH mimicking the MDA reductase catalyzed reaction. These data suggest that dioscorins have both DHA reductase and MDA reductase activities.