A vertebrate fatty acid desaturase with 5 and 6 activities

5 and 6 fatty acid desaturases are critical enzymes in the pathways for the biosynthesis of the polyunsaturated fatty acids arachidonic, eicosapentaenoic, and docosahexaenoic acids. They are encoded by distinct genes in mammals and Caenorhabditis elegans. This paper describes a cDNA isolated from zebrafish (Danio rerio) with high similarity to mammalian 6 desaturase genes. The 1,590-bp sequence specifies a protein that, in common with other fatty acid desaturases, contains an N-terminal cytochrome b5 domain and three histidine boxes, believed to be involved in catalysis. When the zebrafish cDNA was expressed in Saccharomyces cerevisiae it conferred the ability to convert linoleic acid (18:2n-6) and -linolenic acid (18:3n-3) to their corresponding 6 desaturated products, 18:3n-6 and 18:4n-3. However, in addition it conferred on the yeast the ability to convert di-homolinoleic acid (20:3n-6) and eicosatetraenoic acid (20:4n-3) to arachidonic acid (20:4n-6) and eicosapentaenoic acid (20:5n-3), respectively, indicating that the zebrafish gene encodes an enzyme having both 5 and 6 desaturase activity. The zebrafish 5 6 desaturase may represent a component of a prototypic vertebrate polyunsaturated fatty acids biosynthesis pathway.