Generation of pyrophosphate from extracellular ATP at the surface of HeLa cells

On incubation of intact HeLa cells with micromolar concentrations of [gamma 32 P]ATP under physiological conditions, the generation of inorganic pyrophophate in the supernatant has been observed. The reaction depends on incubation time and cell number employed; the enzymatic activity is not shed into the supernatant. Isotope dilution data support that the responsible enzyme(s) is located at the cell surface.