InterPro domain: IPR015876

Fatty acid desaturases are enzymes that catalyse the insertion of a double bond at the delta position of fatty acids. There seems to be two distinct families of fatty acid desaturases which do not seem to be evolutionary related: the first contains stearoyl-CoA desaturase (SCD), also known as Acyl-CoA desaturase or delta-9 desaturase ( 1.14.19.1 ); the second includes plant stearoyl-acyl-carrier protein and cyanobacteria desA protein [ 1 , 2 ].

SCD is a key regulatory enzyme of unsaturated fatty acid biosynthesis. In association with cytochrome b5 and NADP-dependent cytochrome b5 reductase, it constitutes part of a microsomal membrane-bound 3-component system in animals and fungi [ 3 ]. SCD contains 4 putative transmembrane (TM) regions that anchor it in the microsomal membrane [ 4 ]. SCD uses oxygen and electrons from reduced cytochrome b5 [ 5 , 6 , 7 ] to catalyse the insertion of a cis double bond between carbons 9 and 10 of a spectrum of fatty acids [ 8 , 8 , 8 ]. The preferred substrates of SCD are palmitoyl-CoA and stearoyl-CoA, which are converted to palmitoleic (16:1) and oleic (18:1) acids respectively [ 8 , 8 , 8 ]. These unsaturated molecules are the major storage form of fatty acids (as triacylglycerols) in adipocytes [ 8 ].

1. Characterization of delta 9 acyl-lipid desaturase homologues from Arabidopsis thaliana. Plant Cell Physiol 39, 247-53
2. Switching desaturase enzyme specificity by alternate subcellular targeting. Proc Natl Acad Sci U S A 101, 10266-71
3. Differentiation-induced gene expression in 3T3-L1 preadipocytes. Characterization of a differentially expressed gene encoding stearoyl-CoA desaturase. J. Biol. Chem. 263, 17291-300
4. Wheat germ cell-free translation, purification, and assembly of a functional human stearoyl-CoA desaturase complex. Protein Expr Purif 62, 171-8
5. The OLE1 gene of Saccharomyces cerevisiae encodes the delta 9 fatty acid desaturase and can be functionally replaced by the rat stearoyl-CoA desaturase gene. J. Biol. Chem. 265, 20144-9
6. Construction and sequence of cDNA for rat liver stearyl coenzyme A desaturase. J. Biol. Chem. 261, 13230-5
7. Characterization of HSCD5, a novel human stearoyl-CoA desaturase unique to primates. Biochem Biophys Res Commun 332, 735-42