Lipid monolayers: action

The activity of phospholipase A on phosphatidyl choline and phosphatidal choline spread as monolayers on phosphate buffers containing snake venom (Crotalus atrox or Naja naja) was studied by measuring the fall of surface potential as a function of time, pH, film pressure, temperature, and concentrations of phosphate and venom. At 25OC, pH 7.0, and 0.2 fig of venom per ml, optimal activity was observed with both venoms on both substrates at 12 dynes/cm film pressure on 0.04 M phosphate. Under these conditions, the pH optimum for C. atrox was broad (6.6-7.4) and that for N . naja was sharp (8.0) for the action on phosphatidyl choline, whereas both venoms had a sharp optimum at pH 8.0 in their action on phosphatidal choline. The optimal temperature with phosphatidyl choline was 27.5OC for N . naja and 4OoC for C. atrox. In line with studies of phospholipase A activity in bulk phase in ether, phosphatidal choline was attacked much more slowly than phosphatidyl choline by C. atrox. Under conditions where both venoms had equal activity on phosphatidyl choline, C. atrox was only half as active as N . naja on phosphatidal choline. The studies suggest that the linkage of the hydrophobic chains in glycerophosphatides may affect their interaction with proteins.