title: Spectral differences between the alpha and beta heme groups within human deoxyhemoglobin.
abstract: The contributions of the alpha and beta heme groups to the absorbance change that accompanies the aggregation of hemoglobin subunits were measured by comparing the extinction changes produced by n-butyl isocyanide binding to deoxyhemoglobin A with those produced by binding of n-butyl isocyanide to the isolated chains. Almost the entire aggregation absorbance change is associated with the unliganded alpha subunits, which exhibit a 30% increase in molar extinction at 428 nm during tetramer formation. This marked spectral change indicates a substantial perturbation of the electronic properties of the alpha heme groups in going from the high-affinity, isolated chain state to the low-affinity, tetrameric state. The lack of a significant absorbance change as sociated with the beta heme groups implies that the change in reactivity of unliganded beta subunits produced by aggregation is not the result of a change in spin or coordination geometry of the iron atom, but rather involves primarily an alteration in the protein structure near the sixth coordination position.
mesh_terms: D003486:Cyanides; D006418:Heme; D006454:Hemoglobins; D006801:Humans; D008024:Ligands; D010455:Peptides; D011487:Protein Conformation; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship
chemical_list: D003486:Cyanides; D006454:Hemoglobins; D008024:Ligands; D010455:Peptides; D006418:Heme