Effect of Organic Phosphates on the Sulfhydryl Reactivities of Oxyhemoglobins A and S*

The /393 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 p”“ site. Organic phosphatesd ecrease the pg3s ulfhydryl 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 NHa-terminal ends of the p chains