Isolation of a gene encoding 3-isopropylmalate dehydrogenase from rice

3-Isopropylmalate dehydrogenase (IPMDH, EC 1.1.1.85) is a key enzyme in the biosynthesis of leucine and glucosinolates in plants. IPMDH is a bifunctional dimeric enzyme that catalyzes dehydrogenation and decarboxylation reactions in the presence of NAD⁺. The leuB gene encoding IPMDH has been identified in a variety of bacteria and some plants. In this study, we analyze the gene for IPMDH from Oryza sativa (OsIPMDH). The analysis of an EST sequence and rice genome revealed a full-length open reading frame encoding 389 amino acids that correspond to a protein of approximately 41.2 kD. The predicted amino acid sequence of OsIPMDH was highly homologous with the IPMDHs from plants and bacteria. The OsIPMDH expression analysis in a leuB mutant of Escherichia coli revealed that OsIPMDH was capable of functionally complementing the leuB mutant. These results indicate that OsIPMDH encodes for a protein of 3-isopropylmalate dehydrogenase in rice.