o-lodobenzoate interacts non-covalently with hemoglobin and lowers the oxygen affinity of the protein. In contrast to2,3diphosphoglycerate or inositol hexaphosphate, its interaction does not depend upon the presence of free amino groups at theβ-chain amino terminals. Lysineβ82 is one of its oxygenation linked binding sites. As with the organic phosphates, the halogenated benzoate reacts preferentially with deoxy-hemoglobin to shift the allosteric equilibrium from R to T.