A digestive phospholipase A 2 in the tiger beetle Cicindella circumpicta

Abstract

We report on phospholipase A 2 (PLA 2) in the midgut contents of tiger beetles Cicindella circumpicta. PLA 2 is responsible for hydrolyzing fatty acids from the sn-2 position of dietary phospholipids (PLs), an essential step in the digestion and absorption of essential fatty acids. As expected from the background of mammalian digestive PLA 2s, the midgut PLA 2 was Ca 2+-dependent. The PLA 2 in tiger beetle midgut contents was influenced by altering the reaction conditions, including incubation time, protein concentrations, pH and temperature. Routine assay conditions included incubating 3.3 μg of protein prepared from midgut contents in Tris buffer (pH 9.0) for 30 min at 28 °C. Partial purification on size-exclusion chromatography indicated that the molecular weight of the midgut PLA 2 is approximately 22 kDa. The partially purified PLA 2 was inhibited by the site-specific inhibitor oleyoxyethyl phosphorylcholine. The presence of the PLA 2 in the midgut contents is related to feeding activity, because the midgut contents of unfed beetles did not express PLA 2. We suggest that PLA 2s are a common, and quite important, feature of insect digestive physiology.