In animals, desaturation of fatty acids requires a fatty acyl-CoA desaturase (Figure 18.32). The enzyme that creates oleic acid and palmitoleic acid from stearate and palmitate, respectively, is called a -9 enzyme, because it creates a double bond nine carbons from the carboxyl group of the fatty acids. Similar enzymes in mammalian systems include 5 and 6 desaturases, which are under complex hormonal control.

Mammals cannot synthesize double bonds in fatty acids beyond the ninth carbon, so linoleic acid (double bonds at carbons 9 and 12) and linolenic Acid (double bonds at carbons 9,12, and 15) must be provided in mammalian diets.

Linoleic acid is an important precursor of arachidonic acid (Figure 18.33), which is itself a precursor of the prostaglandins and thromboxanes.

1. Fatty Acid Metabolism

2. Prostaglandin and Leukotriene Metabolism