title: Soret spectroscopic and molecular graphic analysis of human semi-beta-hemoglobin formation.
abstract: The interaction of heme-free alpha (alpha(o)) and heme-containing beta (beta(h)) chains of human hemoglobin has been monitored in 0.1 M potassium phosphate buffer, pH 7 or 8, at 5 degrees C. Soret zero and first-derivative spectra were consistent with a uniform association reaction. Stopped-flow investigations demonstrated association rates on the order of 10(7) M(-1) s(-1). This was 100-fold more rapid than the reported rate of combination of alpha(h) and beta(h) proteins. This encounter-like rate of semi-beta-hemoglobin (alpha(o)beta(h)) formation was increased by raising the pH from 7 to 8. pH change is known to affect the spatial arrangement of AB-GH helical entities. Molecular graphic analysis of modeled alpha(o) protein superimposed over native alpha(h) protein revealed an apo Mb-like structure with well-defined AB-GH segments. Repositioning of these core helical segments, resulting in increased conformational freedom of the alpha1beta1 interface, was apparently responsible for the enhanced association properties of the alpha(o) protein.
authors.affiliation: Department of Chemistry, University of Massachusetts Lowell 01854, USA.
authors.forename: F
authors.initials: F
authors.lastname: Chiu
authors.forename: G
authors.initials: G
authors.lastname: Vasudevan
authors.forename: A
authors.initials: A
authors.lastname: Morris
authors.forename: M J
authors.initials: MJ
authors.lastname: McDonald
mesh_terms: D006441:Hemoglobin A / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D011487:Protein Conformation; D021122:Protein Subunits; D013053:Spectrophotometry
chemical_list: D021122:Protein Subunits; D006441:Hemoglobin A