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Group V phospholipase A₂ is a recently discovered secretory phospholipase A₂(PLA₂) that has been shown to be involved in eicosanoid formation in inflammatory cells, such as macrophages and mast cells. We have demonstrated that human group V PLA₂(hsPLA₂-V) can bind phosphatidylcholine (PC) membranes and hydrolyze PC substrates much more efficiently than human group IIa PLA₂, which makes it better suited for acting on the outer plasma membrane (Han, S.-K., Yoon, E. T., and Cho, W. (1998)Biochem. J. 331, 353–357). In this study, we demonstrate that exogenous hsPLA₂-V has much greater activity than does group IIa PLA₂ to release fatty acids from various mammalian cells and to elicit leukotriene B₄ formation from human neutrophils. To understand the molecular basis of these activities, we mutated two surface tryptophans of hsPLA₂-V to alanine (W31A and W79A) and measured the effects of …