Malonyl-CoA abnormal inhibition of residual enzyme activity in carnitine palmitoyltransferase deficiency.

The residual enzyme activity in tissues of a 6-year-old boy with myoglobinuria and carnitine palmitoyltransferase (CPT) deficiency was studied with malonyl-CoA, a specific inhibitor of CPT-I in rat tissues. In this patient the enzyme deficiency was limited to the CPT fraction insensitive to malonyl-CoA, since the residual activity was an increased amount of CPT sensitive to the inhibitor. CPT sensitivity to malonyl-CoA was also assayed in human liver mitochondria, and inhibition was similar to that found in rat liver.