Phospholipase A2 Enzymes

Phospholipase A2 is responsible for the release of arachidonic acid from cell membrane phospholipids. Accordingly, its activity and regulation are important aspects of the generation of prostaglandins and their relatives in various situations, including the protective effects of PGs, as well as in inflammation and others. This enzyme is an obvious therapeutic target although progress in this area has been difficult. Significantly, the secreted enzyme, especially the enzyme found in synovial fluid (s), appears to be a gene product different from the enzyme in cellular cytosol (c). They also differ in catalytic requirements, as shown in Table 16-2. The synovial fluid enzyme consists of 128 amino acids while the cytosolic enzyme is 749 amino acids long, and there is no homology between the two proteins except for a His/Asp pair, which is catalytic in the case of synovial (s) PLA2. Figure 16-8 shows molecular models of porcine pancreatic PLA^ and the position of the Ca2+ ion is indicated in the model. Table 16-3 summarizes physiological processes affected by the phospholipase A2 enzymes.

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