Evidence that multifunctional protein 2, and not multifunctional protein 1, is involved in the peroxisomal beta-oxidation of pristanic acid

The second (enoyl-CoA hydratase) and third (3-hydroxyacyl-CoA dehydrogenase) steps of peroxisomal beta-oxidation are catalysed by two separate multifunctional proteins (MFPs), MFP-I being involved in the degradation of straight-chain fatty acids and MFP-2 in the beta-oxidation of the side chain of cholesterol (bile acid synthesis). In the present study we determined which of the two MFPs is involved in the peroxisomal degradation of pristanic acid by using the synthetic analogue 2-methylpalmitic acid. The four stereoisomers of 3-hydroxy-2-methylpalmitoyl-CoA were separated by gas chromatography after hydrolysis, methylation and derivatization of the hydroxy group with (S)-2-phenylpropionic acid, and the stereoisomers were designated I-IV according to their order of elution from the column. Purified MFP-I dehydrated stereoisomer IV but dehydrogenated stereoisomer III, so by itself MFP-1 is not capable of converting a branched enoyl-CoA into a 3-ketoacyl-CoA. In contrast, MFP-2 dehydrated and dehydrogenated the same stereoisomer (II), so it is highly probable that MFP-2 is involved in the peroxisomal degradation of branched fatty acids and that stereoisomer II is the physiological intermediate in branched fatty acid oxidation. By analogy with the results obtained with the four stereoisomers of the bile acid intermediate varanoyl-CoA, stereoisomer II can be assigned the 3R-hydroxy, 2R-methyl configuration.