The Binding of a Spin-labeled Triphosphate to Hemoglobin

Abstract

In order to understand the molecular nature of cooperative oxygen binding to hemoglobin, it is important to obtain information about the structures of partially oxygenated hemoglobin molecules. Previous applications of the spin-labeling technique (McConnell and McFarland, 1970) to this problem utilized spin labels I and II covalently linked to the β-93 cysteine residues of hemoglobin (Ogawa and McConnell, 1967; Ogawa et al., 1968; McConnell, 1971). Those studies presented evidence for the existence of partially oxygenated hemoglobin molecules having structures distinct from those of hemoglobin and oxyhemoglobin. In addition, it was found that there is a linear relation between protein conformation changes at β-93 and overall heme oxygenation. The latter observation is in agreement with the more recent findings of other investigators (Simon and Cantor, 1969; Antonini and Brunori, 1969).