Human peroxisomal 3-oxoacyl-coenzyme A thiolase deficiency

We investigated the peroxisomal beta-oxidation system in liver from a patient with clinical features similar to those in the cerebrohepatorenal (Zellweger) syndrome and with elevated levels in body fluids of very-long-chain Fatty Acids and intermediates in the biosynthesis of Bile Acids. The peroxisomal beta-oxidation of Fatty Acids, measured as the cyanide-insensitive formation of [14C]acetyl units from [14C]palmitoyl-CoA, was very low in the patient (less than 10% of the values in control subjects). Immunoblotting experiments using antibodies to peroxisomal beta-oxidation Enzymes indicated that peroxisomal 3-oxoacyl-CoA thiolase (acyl-CoA:acetyl-CoA C-acyltransferase, EC 2.3.1.16) was deficient. Addition of purified rat-liver peroxisomal 3-oxoacyl-CoA thiolase to a reaction mixture containing liver homogenate from the patient restored peroxisomal beta-oxidation. We conclude that the deficiency of peroxisomal 3-oxoacyl-CoA thiolase is responsible for the very low peroxisomal beta-oxidation activity and for the accumulation of very-long-chain Fatty Acids and intermediates in the biosynthesis of Bile Acids. Furthermore, the finding that both very-long-chain Fatty Acids and abnormal Bile Acids accumulate in this patient suggests that a single peroxisomal 3-oxoacyl-CoA thiolase is involved in the oxidative chain shortening of both very-long-chain Fatty Acids and the coprostanoic acids.