Can function as a Delta(5) fatty acid desaturase and behaves as a (8-3) desaturase. Introduces a double bond in the fatty acid chain 5 carbons away from carboxy terminal to biosynthesize polyunsaturated fatty acids (PUFAs) endogenously (PUFAs are essential for membrane structure and many cellular and physiological processes). Acts on a variety of substrates such as dihomo-gamma-linoleoyl-CoA ((8Z,11Z,14Z)-eicosatrienoyl-CoA, 20:3n-6) to generate arachidonoyl-CoA ((5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA, 20:4n-6). Also acts on a number of other substrates, including fatty acids that do not contain a double bond at the 8 position like (11Z,14Z,17Z)-eicosatrienoyl-CoA (20:3n-3) to produce (5Z,11Z,14Z,17Z)-eicosatetraenoyl-CoA (20:4n-3). Unlike plants, Caenorhabditis elegans desaturases seem to use fatty acyl-CoAs as substrates.
