Evidence for ecto-protein kinase activity on the surface of human neutrophils

Recent studies have suggested a possible role for extracellular ATP in neutrophil function. This report provides evidence for the existence of an ecto-protein kinase activity on the surface of human neutrophils capable of phosphorylating intrinsic cell membrane proteins as well as exogenous proteins. Addition of extracellular [gamma-32P]ATP to neutrophils resulted in rapid incorporation of 32P into cellular proteins that were sensitive to trypsin. The ability of adherent cells to phosphorylate the exogenous substrate casein, while no protein kinase activity was released into the supernate, provided further evidence for a cell surface associated protein kinase activity.