Tissue polyunsaturated fatty acids and a digestive phospholipase A(2) in the primary screwworm, Cochliomyia hominivorax

We report on the presence of arachidonic acid in larval and adult tissues o f the primary screwworm, Cochliomyia hominivorax and of the secondary screw worm, C. macellaria. Arachidonic acid is present in the phospholipids of wh ole animal extracts of both species. This fatty acid appears to be accumula ted during the larval stages, because proportions of arachidonic acid were higher in adults than in larvae. These insects probably obtain the arachido nic acid from dietary phospholipids. We also report on a phospholipase A(2) activity in midgut preparations from third instars of the primary screwwor m. Phospholipase A(2) is responsible for hydrolyzing fatty acids from the s n-2 position of dietary phospholipids to release essential fatty acids. The screwworm enzyme is similar to mammalian digestive phospholipase A(2)s bec ause it depends on calcium for high catalytic activity, it is sensitive to the site-specific inhibitor oleyloxyethylphosphorylcholine, and it interact s with heparin. We further characterized the screwworm midgut phospholipase A(2) by altering the reaction conditions, including reaction time, radioac tive substrate concentration, protein concentration, pH and temperature. We speculate that the biological significance of this enzyme relates to acqui ring essential fatty acids, including arachidonic acid, from dietary phosph olipids. (C) 1999 Elsevier Science Ltd. All rights reserved.