Isovaleryl-CoA dehydrogenase (IVD, EC ) catalyzes the third step in the catabolism of
leucine in mammals. Deficiency of this
enzyme leads to the clinical disorder
isovaleric acidemia. IVD has been purified and characterized from human and rat liver, and the x-ray crystallographic structure of purified recombinant human IVD has been reported. Nothing is known about IVD activity in plants, although
cDNA clones from Arabidopsis thaliana and partial sequences from Gossypium hirsutum and Oryza sativa have been identified as putative IVDs based on sequence homology and immuno cross-reactivity. In this report we describe the identification and characterization of an IVD from pea, purification of the
enzyme using a novel and rapid
auxin affinity chromatography matrix, and cloning of the corresponding gene. At the
amino acid level, pea IVD is 60% similar to human and rat IVD. The specific activity and abundance of plant IVD was found to be significantly lower than for its human counterpart and exhibits developmental regulation. Substrate specificity of the plant
enzyme is similar to the human IVD, and it cross-reacts to anti-human IVD
antibodies. Molecular modeling of the pea
enzyme based on the structure of human IVD indicates a high degree of structural similarity among these
enzymes. Glu-244, shown to function as the catalytic base in human IVD along with most of the
amino acids that make up the
acyl CoA binding pocket, is conserved in pea IVD. The genomic structure of the plant IVD gene consists of 13 exons and 12 introns, spanning approximately 4 kilobases, and the predicted RNA splicing sites exhibit the extended consensus sequence described for other plant genes.