Leukotrienes are eicosanoids that were originally isolated from leukocytes and contain three double bonds, which explains how they were named. As shown in Figure 19.32, leukotrienes are formed by a pathway independent of that of forming the prostaglandins and thromboxanes.
The pathway to leukotrienes starts by attack on arachidonate of a lipoxygenase, which adds O2 to C-5, giving 5-hydroperoxyeicosatetraenoic acid (5-HPETE). A dehydration to give the epoxide coupled with isomerization of double bonds gives leukotriene A4. Hydrolysis of the epoxide ring yields leukotriene B4. Transfer of the thiol group of glutathione yields leukotriene C4. Subsequent modifications of the peptide chain (not shown) yield related compounds, leukotrienes D and E.
1. Eicosanoids