Anion carrier in the human erythrocyte exists as a dimer

The in situ state of assembly of the human erythrocyte anion carrier (band 3) has been investigated by applying target size analysis on the radiation-induced inactivation of anion flux and degradation of polypeptide band 3. Irradiation with a high energy electron beam resulted in inactivation of carrier-mediated anion flux in intact cells, in inside-out vesicles devoid of cytoskeletal and cytoplasmic proteins, and in inside-out vesicles whose band 3 protein has been partially proteolyzed, with little change in leak pathway. The inactivation showed a single exponential function of radiation dose from which the target size of the anion carrier was estimated to be 210,000, 220,000, and 98,000 daltons in intact cells, in the inside-out vesicles, and in the vesicles after a limited proteolysis, respectively. Irradiation also resulted in degradation of the band 3 of the inside-out vesicles, as detected on sodium dodecyl sulfate-gel electrophoresis, with a dose dependence characteristic of a target size of 220,000 daltons. It is suggested that the human erythrocyte anion carrier exists in situ as a dimer of band 3.