The stimulation of the brain alkaline phospholipase A1 attacking phosphatidylethanolamine by various salts and metal chelators

Rat brain contains a soluble, high molecular weight phospholipase A₁ of alkaline pH optimum which shows a preference for phosphatidylethanolamine as substrate. There is evidence that the same enzyme exists in liver and kidney. At low osmotic concentrations of buffer the enzyme is markedly stimulated by CaCl₂. However, MgCl₂ and MnCi₂ are equally as effective although at concentrations above 2 mM the activation falls away with MnCl₂. The phospholipase A₁ is stimulated by divalent metal ion chelators (EDTA, EGTA, CDTA) and by sodium phosphate and sodium sulphate. The activity is inhibited by hexanol, benzyl alcohol, diethylether and detergents. Although the activity can be inhibited by saturated and unsaturated fatty acids, no evidence could be obtained that the activators function by counteracting the inhibitory action of fatty acids liberated at the interface of the substrate and incubation medium. It is suggested that to achieve good enzymic hydrolysis a certain type of organised hydrated phosphatidylethanolamine structure is required in which the negative zeta potential has been reduced by metallic cations in the incubation medium.