ADP-RIBOSYLATION FACTOR, A SMALL GTP-DEPENDENT REGULATORY PROTEIN, STIMULATES PHOSPHOLIPASE-D ACTIVITY

The hydrolysis of phosphatidylcholine by phospholipase D (PLD) results in the production of phosphatidic acid and choline. An assay that use s an exogenous substrate was developed to measure this activity in mem branes and solubilized preparations from HL60 cells. A cytosolic facto r markedly enhanced PLD activity in membranes and was essential for GT PgammaS-dependent stimulation of an enriched preparation of PLD. The f actor was purified to homogeneity from bovine brain cytosol and identi fied as a member of the ADP-Ribosylation Factor (ARF) subfamily of sma ll G proteins. Subsequently, recombinant myristoylated ARF1 was found to be a better activator of PLD activity than was the nonmyristoylated form. ARF proteins have been implicated recently as factors for regul ation of intracellular vesicle traffic. The current finding suggests t hat PLD activity plays a prominent role in the action of ARF and that ARF may be a key component in the generation of second messengers via phospholipase D.