EVIDENCE FOR THE EXISTENCE OF A PRISTANOYL-COA OXIDASE GENE IN MAN

In the rat, 2-methyl branched fatty acids and the bile acid intermedia tes di- and tri-hydroxycoprostanic acids are desaturated by pristanoyl -CoA oxidase and trihydroxycoprostanoyl-CoA oxidase respectively. In t he human, these compounds are oxidized by a single enzyme, branched-ch ain acyl-CoA oxidase, which according to its amino acid sequence is th e human homologue of rat trihydroxycoprostanoyl-CoA oxidase. Pristanoy l-CoA oxidase is apparently absent from human tissues as indicated by immunoblot analysis [Van Veldhoven, Van Rompuy, Fransen, de Bethune an d Mannaerts (1994) Fur. J. Biochem. 222, 795-801] and Northern-blot an alysis [Vanhooren, Fransen, de Bethune, Baumgart, Baes, Torrekens, Van Leuven, Mannaerts and Van Veldhoven (1996) Fur. J. Biochem. 239, 302- 309] of human tissues. In this paper we present evidence, however, tha t at least the gene for pristanoyl-CoA oxidase is present in the human . A human liver cDNA encoding a protein of 700 amino acids, showing 75 % amino acid identity with rat pristanoyl-CoA oxidase and harbouring a peroxisomal C-terminal-targeting signal (SKL), was isolated. Bacteri al expression of the cDNA resulted in a fusion protein that was cross- reactive with antibodies directed against rat pristanoyl-CoA oxidase a nd the C-terminal SKL sequence. Screening of a genomic library with th e isolated cDNA as a probe resulted in a genomic clone in which four i ntrons were localized. By means of fluorescence in situ hybridization the gene for human pristanoyl-CoA oxidase was mapped at chromosome pos ition 4p15.3. We conclude that a gene for pristanoyl-CoA oxidase is pr esent in the human genome. The gene appears to be expressed to such a low extent in liver that its mRNA cannot be detected by routine Northe rn-blot analysis and that its product remains undetected by standard i mmunoblotting or by enzyme activity measurements. We speculate that th e gene may be expressed under special (e.g. certain developmental stag es) conditions or in certain specialized tissues not examined thus far .