A key and highly regulated enzyme that is required for the biosynthesis of monounsaturated fatty acids is stearoyl-CoA desaturase (SCD), which catalyzes the D9-cis desaturation of a range of fatty acyl-CoA substrates. The preferred substrates are palmitoyl- and stearoyl-CoA, which are converted into palmitoleoyl- and oleoyl-CoA respectively.