Wavelength-dependent spectral changes accompany CN-hemin binding to human apohemoglobin |
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Authors: | Vasudevan G McDonald M J |
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Affiliation: | (1) Biochemistry Program, Department of Chemistry, College of Arts and Sciences, University of Massachusetts, Lowell, Massachusetts, 01854 |
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Abstract: | The interaction of apohemoglobin with two heme derivatives, CN-protohemin and CN-deuterohemin, 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°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 a 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 - and -chain structures. Key differences in the number of stabilizing contacts of the two chains with the peripheral a propionyl 45(CE3); 58(E7); 61(E10) as well as the b 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 dimer interface. |
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Keywords: | CN-hemin binding kinetics apohemoglobin chain heterogeneity wavelength dependence heme peripheral group interactions subunit interface |
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