Inhibition of sulfate transport in Ehrlich ascites tumor cells by 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid(SITS).

The effects of the nonpenetrating amino reactive reagnet 4-acetamido-4'-isothiocyano-stilbene-2-2'-dilsulfonic acid (SITS) on anion transport (sulfate, chloride, and inorganic phosphate) were investigated in Ehrlich ascites tumor cells. Short time exposure to SITS produces a reversible inhibition (92%) of sulfate transport. The kinetics of interaction suggest that reversibly bound SITS competitively inhibits sulfate transport, Ki = 3 X 10(-6)M. Incubation of tumor cells with SITS (1 X 10(-4)M) for longer periods of time results in a time dependent irreversible inhibition of sulfate transport which obeys first order kinetics. The rate coefficient for the inactivation process is 0.040 min-1. The kinetics of irreversible inhibition is best explained by the irreversible binding of SITS to the sulfate transport site, and therefore makes SITS a potentially useful probe for the quantiation of these sites in the tumor cell. The lack of effect of irreversibly bound SITS on either chloride or inorganic phosphate transport points to a specificity in the interaction of SITS with the tumor cell membrane, as well as indicating that an alternate pathway exists for the movement of these anions across the membrane.