The characteristics of phosphate, chloride and sulfate transport across the membrane of the Ehrlich mouse ascites tumor cell suggests that in order for these anions to enter the cell they must first react with specific carrier systems. The purpose of this study is to identify and characterize these anion transport carriers. Since anion transport systems possess no intrinsic markers that are useful in identifying their components, we plan to use probes that irreversibly bind to the membrane and in so doing specifically inhibit anion transport. Of particular interest is the nonpenetrating, amino reactive compound, 4,4'-diisothiocyano stilbene 2,2' disulfonate (DIDS). This agent binds irreversibly to the tumor cell membrane and as a consequence inhibits SO4-2 but not Pi or C lion transport. Tumor cells will be labeled with 3H-DIDS, fractionated and the plasma membrane collected. The purified membrane will be subjected to polyacrylamide gel electrophoresis and the protein bearing the DIDS label characterized in terms of molecular weight, relative abundance and for the presence of carbohydrate. The topographic orientation of the SO4-2 transport site will be studied by utilizing the pyridoxal phosphate-sodium borohydride system to label the cytoplasmic surface of the membrane. This system when used in conjunction with 3H-DIDS labeling of the outer membrane surface will establish whether the SO4-2 transport site spans the membrane. The dynamics of the SO4-2 carrier in terms of its synthesis and degradation will be compared to that of other membrane constituents. Through these efforts we anticipate a more complete understanding of the molecular events associated with the membrane transport of SO4-2, and indeed, other inorganic anions.