Stearoyl-CoA desaturase 5 (SCD5, also known as acyl-CoA desaturase 4), located on the ER membrane, utilises O2 and electrons from reduced ferrocytochrome b5 (Fe(2+)Cb5) to catalyse the insertion of a double bond into a range of fatty acyl-CoA substrates. SCD5 is most abundant in brain and pancreas. The reaction annotated here shows stearoyl-CoA (ST-CoA) desaturation to oleoyl-CoA (OLE-CoA). Studies of tagged recombinant enzyme overexpressed in transiently transfected cells suggest that the enzyme forms dimers and higher oligomers (Wang et al. 2005; Zhang et al. 2005).