SUNY at Albany
June 19-23, 2001
A NMR Investigation of the Energetics of Allosteric Effects in Human Hemoglobin
Previous work from this laboratory has identified three new allosterically sensitive sites in human hemoglobin. Two of these sites, His alpha 103 (G10) and His alpha 122 (H5), are located at the alpha1-beta1 interface and are structurally stabilized in the R (relaxed) relative to the T (tense) state (1). The third site, Trp beta 37 (C3), is located in the hinge region of the alpha1-beta2 interface and is more stable in the T state (2).
In the present work, we have probed the effects of heterotropic allosteric effectors upon the structural free energy changes at these sites. The solvent exchange rates of the side chain NH protons of His alpha 103 (G10), His alpha 122 (H5) and Trp beta 37 (C3) were measured by NMR spectroscopy in the presence of chloride ions, inorganic phosphate ions or the organic phosphate 2,3-DPG. The results indicate that these allosteric effectors selectively affect the exchange rates and/or the local free energy of stabilization at the three sites of interest. The relationship between these findings and the molecular mechanism of allosteric effects in hemoglobin will be discussed.References and Footnotes
Iulian N. Rujan (1), and Irina M. Russu (2),
Department of Molecular Biology and Biochemistry (1), and Department of Chemistry (2), Molecular Biophysics Program, Wesleyan University, Middletown, CT 06459, USA.