Wavelength-dependent spectral changes accompany CN-hemin binding to human apohemoglobin.
The interaction of apohemoglobin with two heme derivatives, CN-protohemin and CN-deutero-hemin, was monitored at multiple Soret wavelengths (417-423 and 406-412 nm, respectively) in 0.05 M potassium phosphate buffer, pH 7.0, at 10 degrees C and revealed, as previously reported, a multiphasic kinetic reaction. Wavelength-dependent reactions were observed for both CN-protohemin and CN-deuterohemin derivatives with the alpha chain (bathochromic entity) displaying faster (4- to 7-fold) rates throughout the courses of both heme-binding reactions. The basis of this spectrally heterogeneous kinetic phenomenon could be deduced from molecular modeling studies of alpha- and beta-chain structures. Key differences in the number of stabilizing contacts of the two chains with the peripheral alpha propionyl 45(CE3); 58(E7); 61(E10) as well as the beta vinyl 38(C4); 71(E15); 106(G8) groups were found. Furthermore, RMS plots comparing apo- and heme-containing subunits reveal substantial structural disparities in the C-CD-F-FG helical regions of the alphabeta dimer interface.
Department of Chemsitry, College of Arts and Sciences, University of Massachusetts, Lowell 01854, USA.
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Vasudevan
M J
MJ
McDonald
D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D019281:Dimerization; D006427:Hemin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D013057:Spectrum Analysis
D001059:Apoproteins; D006454:Hemoglobins; D008024:Ligands; D021122:Protein Subunits; C023478:apohemoglobin; C083499:hemin-CN; C011219:deuterohemin; D006427:Hemin