The activation of surface films of lecithin by amphipathic molecules.

In the preceding paper it was shown that a phospholipase prepared,from Penicllium notatum will hydrolyse lecithin only after the, addition,, of a minimum proportion of anionic amphipathic molecules1 e.g. dicetylphosphoric acid, cardiolipin, sodium dodecyl sulphate (Bangham & Dawson, 1959), The onset of hydrolysis occurred, only when the emulsion particles carried a minimum net negative charge, independent of the .species of anion added. The question arose whether the negative charge on the surface of the emulsion particle was ,directly concerned with the reaction between enzyme,and substrate at the interface, or whether it merely dispersed the substrate more efficiently. This paper attempts to answer this question by a study of the action of the phospholipase on surface films of lecithin and of lecithin containing dicetylphosphoric acid. The technique developed for this study was to float films of [32P]lecithin and to follow the loss of radioactivity from the surface film as the water-soluble glycerylphosphorylcholine produced by the enzyme diffused into the aqueous phase.