Endogenous ADP-ribosylation in human platelets.

We have studied ADP-ribosyltransferase activity in platelet cytosol and electropermeabilized platelets. Cytosolic activity causes ADP-ribosylation or of a 37 kDa protein that is activated by increasing the concentration of potassium phosphate. ADP-ribosylation is inhibited by thiol reagents, an effect partially reversed by cholera toxin. In electropermeabilized platelets incubated with [alpha-32P]NAD, the 37 kDa protein is also ADP-ribosylated as are other proteins and albumin. Under these conditions, ADP-ribosylation is partially inhibited by nicotinamide. This experimental design could be used to determine the effect of cell agonists on endogenous ADP-ribosylation of proteins.