Cloning and characterization of the Bambusa oldhamii BoMDH-encoded malate dehydrogenase.

Malate dehydrogenase (MDH), which is ubiquitously occurred in nature, catalyzes the interconversion of malate and oxaloacetate. Higher plants contain multiple forms of MDH that differ in coenzyme specificity, subcellular localization and physiological function. A putative Bambusa oldhamii BoMDH cDNA was screened with the specific probe from the bamboo cDNA library. Sequence alignment shows that there's a high homology between the deduced amino acid sequence of BoMDH and MDH protein in Oryza sativa glyoxysome (92%). A 57 kDa fusion protein was expressed by IPTG induction in Escherichia coli BL21 (DE3), and an obvious MDH activity was detected in the recombinant protein. The molecular mass of recombinant BoMDH was estimated to be 120 kDa, and the subunit form was 57 kDa by denatured SDS-PAGE, indicating that BoMDH presents as a homodimer. The optimum temperature and pH for BoMDH activity were 40 °C and 9.5, respectively. The K_m values of BoMDH for malate and NAD⁺ were 5.2 mM and 0.52 mM. The k_cat/K_m values of BoMDH for malate and NAD⁺ were 163 min^-1 mM^-1 and 3,060 min^-1 mM^-1.