Regulation of early endosome fusion by phospholipase D activity

In vitro or cell-free assays of homotypic fusion between early endosomes have provided several insights into the means by which an intracellular membrane fusion event can be regulated. In this report we show that homotypic fusion between early endosomes from baby-hamster kidney cells is partially blocked by 340 mM ethanol (2% v/v) and by 100 mM butan-1-ol, but not by the secondary alcohol butan-2-ol. We ascribe the effect of primary alcohols to their participation in a well-characterised transphosphatidylation reaction catalysed by phospholipase D activity, which results in the production of phasphatidylalcohol at the expense of phosphatidic acid. In accordance with this interpretation, we find that addition of exogenous phospholipase D results in stimulation of early endosome fusion.