DEFECT IN BIOSYNTHESIS OF MITOCHONDRIAL ACETOACETYL COENZYME-A THIOLASE IN CULTURED FIBROBLASTS FROM A BOY WITH 3-KETOTHIOLASE DEFICIENCY

The etiology of 3-ketothiolase deficiency has been attributed to a defect of mitochondrial acetoacetyl-CoA thiolase because the acetoacetyl-CoA thiolase activity in related materials is not activated by K+, a property characteristic for this enzyme. We studied the enzymes protein and the biosynthesis of mitochondrial acetoacetyl-CoA thiolase, using cultured skin fibroblasts from a 5-yr-old boy with 3-ketothiolase deficiency. The following results were obtained. Activation of acetoacetyl-CoA thiolase activity by K+ was nil; The enzyme activity was not affected by treatment with the antibody against mitochondrial acetoacetyl-CoA thiolase; A signal for mitochondrial acetoacetyl-CoA thiolase protein was not detected in the immunoblot analysis; and Pulse-chase experiments of skin fibroblasts, using [35S]methionine, revealed no incorporation of radioactivity into this enzyme. Therefore, fibroblasts from this patient lacked mitochondrial acetoacetyl-CoA thiolase protein due to a defect in its biosynthesis.