No abstract

Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via ␤-oxidation. A defect in peroxisomal ␤-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo -oxidation, which may provide an alternative route for the breakdown of VLCFAs. The -oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce -hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from -hydroxy-VLCFAs. We demonstrate that very-longchain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD ؉ -dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjögren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of -hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of -hydroxy-VLCFAs occurs predominantly via the NAD ؉ -dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids.-Sanders, R.-J., Ofman, R., Dacremont, G., Wanders, R. J. A., Kemp, S. Characterization of the human -oxidation pathway for -hydroxy-very-long-chain fatty acids. FASEB J. 22,