The CoA esters of 2-methyl-branched chain fatty acids and of the bile acid intermediates di- and trihydroxycoprostanic acids are oxidized by one single peroxisomal branched chain acyl-CoA oxidase in human liver and kidney.

Rat liver peroxisomes contain three acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins; pristanoyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids (e.g. pristanic acid); and trihydroxycoprostanoyl-CoA oxidase, which oxidizes the CoA esters of the bile acid intermediates di- and trihydroxycoprostanic acids (Van Veldhoven, P. P., Vanhove, G., Asselberghs, S., Eyssen, H. J., and Mannaerts, G. P. (1992) J. Biol. Chem. 267, 20065-20074). In the present report we demonstrate that human liver peroxisomes contain only two acyl-CoA oxidases: palmitoyl-CoA oxidase, which oxidizes the CoA esters of straight chain fatty acids and prostaglandins, and a novel branched chain acyl-CoA oxidase, which oxidizes the CoA esters of 2-methyl-branched fatty acids as well as those of the bile acid intermediates (which also possess a 2-methyl substitution in their side chains). The branched chain acyl-CoA oxidase was purified to near homogeneity by means of column chromatography. It appeared to be a 70-kDa monomeric protein that did not cross-react with antisera raised against rat palmitoyl-CoA oxidase and pristanoyl-CoA oxidase. No indication was found for the presence of a separate trihydroxycoprostanoyl-CoA oxidase in human liver. The branched chain acyl-CoA oxidase was present also in human kidney, suggesting that it is expressed in other extrahepatic tissues as well. Our results explain a number of clinical-chemical observations made in certain cases of peroxisomal beta-oxidation disorders.