A vertebrate fatty acid desaturase with Δ5 and Δ6 activities

Δ5 and Δ6 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 Δ6 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 α-linolenic acid (18:3n-3) to their corresponding Δ6 desaturated products, 18:3n-6 and 18:4n-3. However, in addition it conferred on the yeast the ability to convert di-homo-γ-linoleic 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 Δ5 and Δ6 desaturase activity. The zebrafish Δ5/Δ6 desaturase may represent a component of a prototypic vertebrate polyunsaturated fatty acids biosynthesis pathway.