Yam Tuber Storage Protein Reduces Plant Oxidants Using the Coupled Reactions as Carbonic Anhydrase and Dehydroascorbate Reductase

Abstract

Dioscorin is the major storage protein of yam tuber and accounts for approximately 80%–85% of the total soluble proteins. The protein also exhibits the activities of carbonic anhydrases (CAs) (Hou et al., 1999b, 2000) and dehydroascorbate (DHA) reductases (Hou et al., 1999a). CAs are zinc metalloenzymes that catalyze the interchange of CO2 and HCO3–. There are at least four distinct CA subfamilies: α, β, γ, and δ, with no significant amino acid sequence identities. It is interesting that the amino acid sequence of plant-sourced dioscorin indicates that the protein is closer to the α-CAs of animals than to plant β-CAs (Hewett-Emmett and Tashian, 1996).