Soret spectroscopic and molecular graphic analysis of human semi-beta-hemoglobin formation.
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.
Chiu
F
F
Department of Chemistry, University of Massachusetts Lowell 01854, USA.
Vasudevan
G
G
Morris
A
A
McDonald
M J
MJ
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
D021122:Protein Subunits; D006441:Hemoglobin A