Delta(9)-fatty acid desaturase that acts preferentially on palmitoyl-CoA (hexadecanoyl-CoA) producing the monounsaturated palmitoleoyl-CoA ((9Z)-hexadecenoyl-CoA), which can be elongated to (11Z)-octadecenoyl-CoA (the most abundant monounsaturated fatty acid in Caenorhabditis elegans phospholipids and triacylglycerols). Also acts on pentadecanoyl-CoA, heptadecanoyl-CoA and myristoyl-CoA (tetradecanoyl-CoA), the monounsaturated fatty acids (MUFAs) produced are further used as substrates to synthesize polyunsaturated fatty acids (PUFAs) by several other desaturases and elongases (PubMed:16839188, PubMed:10872837, PubMed:29237573). Unlike plants, Caenorhabditis elegans desaturases seem to use fatty acyl-CoAs as substrates (By similarity). 2 Fe(II)-[cytochrome b5] + 2 H(+) + hexadecanoyl-CoA + O2 = (9Z)-hexadecenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 + tetradecanoyl-CoA = (9Z)-tetradecenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + heptadecanoyl-CoA + O2 = (9Z)-heptadecenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 + pentadecanoyl-CoA = (9Z)-pentadecenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O Lipid metabolism; monounsaturated fatty acid biosynthesis. Expressed in the intestine in adult worms and in all four larval stages. Additional expression in the pharynx and tail cells after hatching and throughout the lifespan. Expression is regulated by nhr-80 and nhr-49 in the intestine. The histidine box domains may contain the active site and/or be involved in metal ion binding. Cytochrome b5 CYTB-5.2 is specifically required for the desaturase activity, its knockdown or mutation alters the enzyme activity. Belongs to the fatty acid desaturase type 1 family.