Demonstration of a specific mitochondrial isovaleryl-CoA dehydrogenase deficiency in fibroblasts from patients with isovaleric acidemia.

Abstract

To study the enzymatic basis of isovaleric acidemia, assay methods for isovaleryl-CoA and butyryl-CoA dehydrogenases that measure amount of tritium released from the respective [2,3-3H]acyl CoA were developed. Because assay of these enzymes in human fibroblast homogenates was subject to interference by nonspecific reactions, mitochondria from cultured skin fibroblasts were isolated by protease treatment, homogenization and differential centrifugation. By using this assay method with these isolated mitochondria, a specific deficiency of isovaleryl-CoA dehydrogenase activity in cultured skin fibroblasts from 5 patients with isovaleric acidemia was demonstrated. Mitochondrial butyryl-CoA dehydrogenase (EC 1.3.99.2) activity in these cells was preserved at normal levels. These results were reproduced by using the conventional dye reduction assays. These observations give further support to the hypothesis that isovaleryl CoA is dehydrogenated by a specific enzyme and that isovaleric acidemia is due to deficiency of this enzyme.