Abstract:A cDNA encoding a putative monodehydroascorbate reductase (MDAR) was cloned from sweet potato. The deduced protein showed high level of sequence homology with MDARs from other plants or related family from bacteria (23~80%). A 3-D homology structure was created for this MDAR. Functional sweet potato MDAR was expressed and purified. The purified enzyme showed an active monomeric form on a 10% native PAGE. The protein's half-life of deactivation at 70℃ was 12.4 min, and its thermal inactivation rate constant K(subscript d) was 5.6×10^(-2) min^(-1). The enzyme was stable in a broad pH range from 6.0-10.0, and in the presence of 0.8 M imidazole. The K(subscript m) value for monodehydroascorbate (MDA) and NADH were 21.1 and 39.7 μM, respectively.