Phospholipases A and B activities of the oriental hornet ( Vespa Orientalis) venom and venom apparatus

Abstract

Phospholipases A and B activities of the oriental hornet ( Vespa orientalis) venom and venom apparatus. Toxicon 15, 141–156, 1977.—Oriental hornet venom is a rich source of both phospholipase A (PhA) and phospholipase B (PhB) activities. This was shown by incubating venom with egg yolk or with pure lecithin and lysolecithin. Activity was measured by titrating liberated fatty acids and by phosphorus analyses of separated phospholipids from thin-layer chromatographic plates. Both lecithin and lysolecithin were rapidly hydrolyzed by venom at pH 4 and 8. With egg yolk as substrate, the optimum Ph activity was observed at pH 5 although considerable activity was observed from pH 3·5 to 9·5. In contrast purified substrates showed greater activity at an alkaline pH, whether assay was in the presence of collidine-acetate or Tris buffer or in the presence or absence of ether. Ether dramatically changed the optimal pH for Ph activity, with egg yolk as substrate, from acidic to alkaline. It is not known whether these PhA and PhB activities are dual activities of a single enzyme or activities of two separate enzymes. The venom has neither PhC nor lipase activities. PhA and PhB activities were observed not only in pure venom (V), but also in venom sacs (VS) where the venom is stored, in the acid (venom) glands (H +) where the venom is produced, and in the alkaline (Dufours) gland (OH −) whose function is unknown. The release of free fatty acids from egg yolk at pH 5 was in the ratios of 1 (V): 0·13 (VS): 0·04 (H +): 0·30 (OH −). Measurements of Ph activities in combinations of the above preparations showed that strong activators or inhibitors of the enzyme are not present. The mid-gut, fat body and hemolymph of the hornet showed Ph activity only equal to about one-half of one per cent of that of the OH − gland. Antisera produced against V, VS, H + and OH − were cross-reactive and inhibited to varying degrees the Ph activities of each of the above preparations. The highest titre antisera were produced in rabbits injected with V or VS, in contrast to the low titres produced with H + and OH − glands. Low Ph activity is detectable in the venom sacs 2 days prior to emergence, with 20-fold higher activities being observed at 5 days of age. The oriental hornet may be extremely useful as a rich source of not only PhA but also PhB activities. The effects of this latter enzyme on biological systems have not been thoroughly evaluated. The drastic disruption of phospholipid structure and hydrophobic binding forces between phospholipid and protein, by the combined PhA plus PhB activities, may be responsible for some of the pharmacological actions of hornet venom.