A COMMON ANCESTOR FOR CANDIDA-TROPICALIS AND DEHYDROGENASES THAT SYNTHESIZE ANTIBIOTICS AND STEROIDS

Candida tropicalis peroxisomes contain a 905-residue trifunctional enzyme with hydratase-dehydrogenase-epimerase activity that is important in fatty acid β-oxidation. At its amino terminus are two tandem copies of an ~280 residue domain of unknown function. We provide evidence that this domain is homologous to oxidoreductases used for metabolizing sugars and synthesizing antibiotics and steroids such as estradiol, androstenedione, corticosterone, and hydrocortisone. The trifunctional enzyme shows no sequence similarity to the bifunctional hydratase-dehydrogenase found in animal peroxisomes and plant glyoxysomes, which are homologs of each other. We suggest that the C. tropicalis trifunctional enzyme and the animal and plant bifunctional enzymes have different ancestors.