NH2-terminal spin labeling of human hemoglobin--spin states and temperature dependence.
In order to explore fully how ligand- and temperature-induced alterations in the spin states of heme iron are related to protein readjustments, the spin label 4-isothiocyanate (I) was covalently attached at beta-93 cysteines and at NH2-terminal valines of various heme-iron ligand forms of human hemoglobin. It was found that the mobility of NH2-terminally bound spin labels depends on the magnetic moment of the heme iron. There is a an approximately linear relationship between the magnetic moment of the heme iron and the mobility of NH2-terminally bound spin labels. In accordance with our previous results, the temperature dependence of ESR spectra of spin-labeled hemoglobin suggests the temperature-induced protein conformational change in those heme-iron ligand forms that are characterized by the equilibrium of the spin states of the heme iron. The conformational change was sensed at both spin-label-binding sites: at beta-93 cysteines and at NH2-terminal valines.
D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006418:Heme; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D017879:Isothiocyanates; D007700:Kinetics; D011487:Protein Conformation; D013816:Thermodynamics; D013861:Thiocyanates
D006454:Hemoglobins; D017879:Isothiocyanates; D013861:Thiocyanates; C037152:isothiocyanic acid; D006418:Heme