A digestive phospholipase A-2 in the tiger beetle Cicindela circumpicta
Uscian, J.M.; Miller, J.S.; Sarath, G.; Stanley Samuelson, D.W.
Journal of Insect Physiology 41(2): 135-141
ISSN/ISBN: 0022-1910 DOI: 10.1016/0022-1910(94)00094-w
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 mu-g of protein prepared from midgut contents in Tris buffer (pH 9.0) for 30 min at 28 degree 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.