A phospholipase A1 from the hemolymph of the tobacco hornworm, Manduca sexta.

Hemolymph (blood) of an insect, the tobacco hornworm, Manduca sexta, contains a phospholipase A1. The specificity of this enzyme was demonstrated by the use of substrates with labeled fatty acids in specific positions and by conversion of the enzyme product, a lysophospholipid, to 2-acylglycerol by the action of bacterial phospholipase C. The insect phospholipase A1 hydrolyzes phosphatidylethanolamine and phosphatidylglycerol, but not phosphatidylcholine or triolein. Divalent cation is required, with calcium ion being most effective, although strontium, barium, and magnesium ions also support activity. Only substrates dispersed in buffer from ethanol are hydrolyzed; ether, Triton X-100, and taurodeoxycholate are inhibitory. The enzyme has been purified 90-fold. At that stage, it is still far from homogeneous, but stability problems have hindered further purification. It has an apparent Mr = 155,000 +/- 11,000, estimated by gel permeation chromatography.