Protein thiophosphorylation associated with secretory inhibition in permeabilized chromaffin cells

Permeabilized cells treated with the adenosine triphosphate analog, [35S]adenosine-5'-0-(3-thiotriphosphate) ([gamma-35S]ATP), showed thiophosphorylation of a small number of cellular proteins. A 54 kilodalton (kDa) protein was heavily thiophosphorylated in unstimulated control cells and a 43 kilodalton protein was more heavily thiophosphorylated in calcium stimulated cells. Intact cells incorporated 35S into a series of higher molecular weight proteins. Stimulation of prelabelled, permeabilized cells resulted in a loss of 35S from the cells over a 20 min period. Treatment of permeabilized cells with ATP gamma S inhibited secretion and 35S incorporation into the cells. Pretreatment with ATP gamma S resulted in subsequent inhibition of both secretion and the ability of the cells to incorporate 35S from [gamma-35S]ATP. These results indicate that the sites normally available for phosphorylation were inactivated by thiophosphorylation and were unavailable to participate in the secretory process. The inhibition of secretion associated with thiophosphorylation of these proteins suggests that they may play a role in the control of secretion by chromaffin cells.