Reinvestigation of peroxisomal 3-ketoacyl-CoA thiolase deficiency: identification of the true defect at the level of d-bifunctional protein

In this report, we reinvestigate the only patient ever reported with a deficiency of peroxisomal 3-ketoacyl-CoA thiolase (THIO). At the time when they were described, the abnormalities in this patient, which included accumulation of very-long-chain fatty acids and the bile-acid intermediate trihydroxycholestanoic acid, were believed to be the logical consequence of a deficiency of the peroxisomal β-oxidation enzyme THIO. In light of the current knowledge of the peroxisomal β-oxidation system, however, the reported biochemical aberrations can no longer be explained by a deficiency of this thiolase. In this study, we show that the true defect in this patient is at the level of d-bifunctional protein (DBP). Immunoblot analysis revealed the absence of DBP in postmortem brain of the patient, whereas THIO was normally present. In addition, we found that the patient had a homozygous deletion of part of exon 3 and intron 3 of the DBP gene, resulting in skipping of exon 3 at the cDNA level. Our findings imply that the group of single–peroxisomal β-oxidation–enzyme deficiencies is limited to straight-chain acyl-CoA oxidase, DBP, and α-methylacyl-CoA racemase deficiency and that there is no longer evidence for the existence of THIO deficiency as a distinct clinical entity

Molecular cloning and expression of human L-pipecolate oxidase

In higher eukaryotes L-lysine can be degraded via two distinct routes including the saccharopine pathway and the L-pipecolate pathway. The saccharopine pathway is the primary route of degradation of lysine in most tissues except the brain in which the L-pipecolate pathway is most active. L-pipecolate is formed from L-lysine via two enzymatic reactions and then undergoes dehydrogenation to Delta(1)-piperideine-6-carboxylate. At least in humans and monkeys, this is brought about by the enzyme L-pipecolate oxidase (PIPOX) localized in peroxisomes. In literature, several patients have been described with hyperpipecolic acidaemia. The underlying mechanism responsible for the impaired degradation of pipecolate has remained unclear through the years. In order to resolve this question, we have now cloned the human L-pipecolate oxidase cDNA which codes for a protein of 390 amino acids and contains an ADP-betaalphabeta-binding fold compatible with its identity as a flavoprotein. Furthermore, the deduced protein ends in -KAHL at its carboxy terminus which constitutes a typical Type I peroxisomal-targeting signal (PTS I

Molecular basis of Sjögren-Larsson syndrome: frequency of the 1297-1298 del GA and 943C>T mutation in 29 patients

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