Identification of the pathway of alpha-oxidation of cerebronic acid in peroxisomes.

Abstract

Cerebronic acid (2-hydroxytetracosanoic acid), an alpha-hydroxy very long-chain fatty acid (VLCFA) and a component of cerebrosides and sulfatides, is unique to nervous tissues. Studies were carried out to identify the pathway and the subcellular site involved in the oxidation of cerebronic acid. The results from these studies revealed that cerebronic acid was catabolized by alpha-oxidation to CO2 and tricosanoic acid (23:0). Studies with subcellular fractions indicated that cerebronic acid was alpha-oxidized in fractions having particulate bound catalase and enzyme systems for the beta-oxidation of VLCFA (e.g., lignoceric acid), suggesting peroxisomes as the subcellular organelle responsible for alpha-oxidation of cerebronic acid. Etomoxir, an inhibitor of mitochondrial fatty acid oxidation, had no effect on cerebronic acid alpha-oxidation. Further, cerebronic acid oxidation was found to be dependent on the presence of NAD+ but not FAD, NADPH, ATP, Mg2+, or CoASH. Intraorganellar localization studies indicated that the enzyme system for the alpha-oxidation of cerebronic acid was associated with the peroxisomal limiting membranes. Studies on cultured fibroblasts from normal subjects and patients with peroxisomal disorders indicated an impairment of alpha-oxidation of cerebronic acid in cell lines that lack peroxisomes [e.g., Zellweger syndrome (ZS)]. On the other hand, alpha-oxidation of cerebronic acid was found to be normal in cell lines from X-linked adrenoleukodystrophy, adult Refsum disease, and rhizomelic chondrodysplasia punctata. Our results clearly demonstrate that alpha-oxidation of alpha-hydroxy VLCFA (cerebronic acid) is a peroxisomal function and that this oxidation is impaired in ZS. Furthermore, this alpha-oxidation enzyme system is distinct from the one for the alpha-oxidation of beta-carbon branched-chain fatty acids (e.g., phytanic acid).