title: Comparison of enzymatic and pharmacological activities of lysine-49 and aspartate-49 phospholipases A2 from Agkistrodon piscivorus piscivorus snake venom.
abstract: The basic Lys-49 phospholipase A2 (PLA2) from Agkistrodon piscivorus piscivorus venom is homologous to the basic Asp-49 PLA2 from the same venom as well as other snake venom PLA2 enzymes. It differs, however, in several respects, most important being replacement of the previously invariant Asp-49 at the calcium binding site by Lys, resulting in a reversed order of addition of calcium and phospholipid, phospholipid binding first. Although the preferences for phospholipid substrates of the two enzymes are identical, the apparent Vmax of the Lys-49 PLA2 was only 1.4 to 3% that of the Asp-49 enzyme. Similarly, the Lys-49 PLA2, compared to the Asp-49 PLA2 had less than 3% of the intraventricular lethal potency and 4% of the anticoagulant activity. The intravenous lethal potency of the Lys-49 enzyme was 20% that of the Asp-49 PLA2 and both had little direct hemolytic activity. In contrast, both enzymes were approximately equipotent on the phrenic nerve-diaphragm preparation and on the isolated ventricle strip of the heart. On the cardiac and neuromuscular preparations, the effects of the Asp-49 PLA2 were accompanied by hydrolysis of phosphatidylcholine and phosphatidylethanolamine, whereas no phospholipid hydrolysis was observed with the Lys-49 PLA2. Evaluation of the present results, along with earlier findings using Asp-49 PLA2 enzymes from Naja nigricollis, Hemachatus haemachatus and Naja naja atra venoms, allows us to conclude that: The A. p. piscivorus Asp-49 PLA2 enzyme resembles the Asp-49 enzymes from N. n. atra and H. haemachatus. In contrast, the A. p. piscivorus Lys-49 PLA2 has much lower enzymatic and anticoagulant activities than the Asp-49 enzymes, but equal cardiotoxic and junctional effects. In contrast to some previous suggestions, basic PLA2 enzymes are not necessarily more toxic than neutral or acidic enzymes. Pharmacological effects upon the heart and phrenic nerve-diaphragm preparation correlate neither with in vitro measurements of PLA2 activity nor with actual levels of phospholipid hydrolysis in the heart or diaphragm. This suggests that PLA2 enzymes exert effects independent of phospholipid hydrolysis.
mesh_terms: D000818:Animals; D001224:Aspartic Acid; D001777:Blood Coagulation / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D003435:Crotalid Venoms / Q000378:metabolism*; D006321:Heart / Q000187:drug effects; D006461:Hemolysis; D007700:Kinetics; D008239:Lysine; D051379:Mice; D009469:Neuromuscular Junction / Q000187:drug effects; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism* / Q000633:toxicity; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D051381:Rats
chemical_list: C031442:Agkistrodon venoms; D003435:Crotalid Venoms; D010743:Phospholipids; D001224:Aspartic Acid; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D008239:Lysine; D002118:Calcium