Evidence for histidine in the triethyltin-binding site of rat haemoglobin.

One molecule of rat haemoglobin binds two molecules of triethyltin. The binding sites are located on the globin and there is co-operativity between the sites such that the intrinsic affinity constant at pH8.0 increases from 3.5x10(5)m(-1) for the binding of the first triethyltin molecule to 5.0x10(5)m(-1) for the binding of the second. Evidence is presented, from pH studies and the kinetics of inhibition due to photo-oxidation, that each binding site contains two histidine residues.