Band 3-hemoglobin associations. The band 3 tetramer is the oxyhemoglobin binding site

The associations between the band 3 protein of the human erythrocyte membrane and oxyhemoglobin, in solutions of a nonionic detergent, were studied by sedimentation equilibrium experiments in the analytical ultracentrifuge. The following results were obtained: (i) hemoglobin is bound virtually exclusively to the band 3 tetramer, but not to the monomer or dimer; (ii) the band 3 tetramer can bind up to four hemoglobin tetramers; (iii) unlike the unstable dimers of unmodified band 3, stable dimers crosslinked via S-S-bridges also represent hemoglobin binding sites.