Molecular Cloning and Sequence Analyses of Rat Liver Dihydroorotate Dehydrogenase

Abstract

Dihydroorotate dehydrogenase (DHOdehase) catalyzes the fourth step of de novo pyrimidine synthesis, the conversion of dihydroorotate to orotate. DHOdehase diverges in many aspects from the other enzymes of UMP biosynthesis: In mammals the enzyme is located in the inner mitochondrial membrane whereas the CAD protein and the UMP synthase are cytosolic. It is the only redox reaction of this pathway and is linked to the respiratory chain via ubiquinone. The enzymes of de novo pyrimidine synthesis are organized as multifunctional proteins that arose through ancestral gene fusions and DHOdehase is the only monoenzymic protein of the pathway. Biochemical and structural characteristics of mammalian DHOdehase are not fully understood, nor are details of its gene regulation known so far. The genes of different mammalian CAD proteins and UMP synthases have been cloned and mapped to different chromosomes. The sole sequence information concerning mammalian DHOdehases available so far is the truncated cDNA encoding for human DHOdehase¹. Recently the rat and porcine enzymes were purified and characterized in our lab^2-4. In order to further investigate structural characteristics of the protein, the cDNA of rat liver DHOdehase was cloned and analysed.