Lecithin-lysolecithin cycle in the toad bladder

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Abstract
Metabolism of lecithin and lysolecithin was explored in homogenates of toad-bladder epithelium. Using biosynthetically labeled lecithin-and lysolecithin-32p as substrates, the presence was established of the reactions: lecithin[forward arrow] lysolecithin and lysolecithin[forward arrow] lecithin. Lecithinase activity with almost exclusive formation of lysolecithin is maximal at pH 7.0 and evident towards both endogenous and added lecithin. Conversion of lysolecithin to lecithin is also optimal at pH 7.0, requires addition of CoA [coenzyme A], and is attributable to direct acylation. Thus, enzymes of a lecithin-lysolecithin cycle are present in toad-bladder epithelium. It is speculated that the production of the potent membrane-lytic agent lysolecithin and its removal by reconversion to lecithin may relate to changes in permeability.