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Anticoagulant Activitv and Plasma Phosphatidvlserine ~ydrol6is by Snake venom ~hospholipases A; Dear Sir, We based our view that the anticoagulant effect of phospholipases A2 (PLA,) is not due to their catalytic activity on: a) the lack of correlation between hydrolysis of the main plasma phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and anticoagulant potency (1) and b) on the selective effects of chemical modifications of PLA2 on these two parameters (2, 3). Boffa et al. (4) questioned our conclusions pointing out that phosphatidylserine (PS), the main procoagulant phospholipid contributed by the platelets, was not assayed being below the limit of detection of our method. We now increased the amounts of PS in the system by supplementing plasma with an excess of platelets. factors in platelets and red blood cells: observations on their chemical nature and function on in vitro coagulation.

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SummaryThe anticoagulant effects and the simultaneous plasma phospholipid hydrolysis induced by three purified phospholipases obtained from snake venoms, i.e., the basic, relatively toxic N. nigricollis, the neutral, relatively nontoxic H. haemachatus, and the acidic, relatively nontoxic N. n. atra, have been compared. The N. nigricollis phospholipase has a very strong anticoagulant effect at concentrations which induce relatively low levels of phospholipid hydrolysis in plasma. The H. haemachatus and N. n. atra phospholipases become anticoagulant only at high concentrations, and the associated phospholipid hydrolysis is also very high. It is concluded that, while all phospholipases are likely to inhibit coagulation if used in amounts sufficiently large to deplete plasma of phospholipids, strongly active phospholipases, such as N. nigricollis, interfere nonenzymatically with the clotting process before any appreciable phospholipid hydrolysis is reached.

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