Effect of organic phosphates on the sulfhydryl reactivities of oxyhemoglobins A and S.

The beta 93 sulfhydryl groups of oxyhemoglobins A and S display a difference in reactivity with 5,5'-dithiobis-2-nitrobenzoic acid. It is concluded that this difference arises from differences in tertiary structure in the vicinity of the beta 93 site. Organic phosphates decrease the beta 93 sulfhydryl reactivity. We have used this effect to measure the organic phosphate binding constants. Hemoglobin S binds organic phosphates very weakly compared to hemoglobin A. This result indicates that the structure at the organic phosphate binding site is different in the two oxyhemoglobins and may be the result of differences in the structure of the NH2-terminal ends of the beta chains.