You are examining the lipid synthesis characteristics of mixed cell types in culture. You find that the cells normally activate PLA2 and that you can detect the synthesis of the intermediate 15S-H(p) ETE. However, in this system you cannot detect the subsequent production of LXA4. Which of the following enzymes is most likely not functional in this culture system?

Question

Quizplus · Accepted Answer

5-LOX is the enzyme that is responsible for the synthesis of LXA4. Since LXA4 is not being produced in this system, it is likely that 5-LOX is not functional. In one of the classical pathways of lipoxin synthesis the interactions between epithelial cells and leukocytes requires the activities of both 15-LOX and 5-LOX. Within the epithelial cells, the PLA₂-mediated release of arachidonic acid serves as a substrate for 15-LOX and generates 15S-H(p) ETE. This latter compound will then diffuse out of the epithelial cells and be taken up by leukocytes where the activity of 5-LOX will then convert it into 15S-epoxytetraene, which is the precursor for LXA₄ synthesis. Therefore, the presence of upstream activities and lipid products in the absence of LXA₄ synthesis indicates that there is a defect in the activity of 5-LOX in this system.

You Are Examining the Lipid Synthesis Characteristics of Mixed Cell