Stearoyl-CoA desaturase (SCD; EC 188.8.131.52) is an iron-containing enzyme that catalyzes a rate-limiting step in the synthesis of unsaturated fatty acids. The principal product of SCD is oleic acid, which is formed by desaturation of stearic acid. The ratio of stearic acid to oleic acid has been implicated in the regulation of cell growth and differentiation through effects on cell membrane fluidity and signal transduction. Four SCD isoforms, Scd1 through Scd4, have been identified in mouse. In contrast, only 2 SCD isoforms, SCD1 and SCD5 (MIM 608370), have been identified in human. SCD1 shares about 85% amino acid identity with all 4 mouse SCD isoforms, as well as with rat Scd1 and Scd2. In contrast, SCD5 shares limited homology with the rodent SCDs and appears to be unique to primates.
Elevated expression levels of SCD1 is found to be correlated with obesity  and tumor malignancy. It is believed that tumor cells obtain most part of their requirement for fatty acids by de novo synthesis. This phenomenon depends on increased expression of fatty acid biosynthetic enzymes that produce required fatty acids in large quantities.
SCD1 function has also been shown to be involved in germ cell determination, adipose tissue specification, liver cell differentiation and cardiac development.
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