Quaternary structures of intermediately ligated human hemoglobin a and influences from strong allosteric effectors: resonance Raman investigation.
The Fe-histidine stretching (nu(Fe-His)) frequency was determined for deoxy subunits of intermediately ligated human hemoglobin A in equilibrium and CO-photodissociated picosecond transient species in the presence and absence of strong allosteric effectors like inositol(hexakis)phosphate, bezafibrate, and 2,3-bisphosphoglycerate. The nu(Fe-His) frequency of deoxyHb A was unaltered by the effectors. The T-to-R transition occurred around m = 2-3 in the absence of effectors but m > 3.5 in their presence, where m is the average number of ligands bound to Hb and was determined from the intensity of the nu(4) band measured in the same experiment. The alpha1-beta2 subunit contacts revealed by ultraviolet resonance Raman spectra, which were distinctly different between the T and R states, remained unchanged by the effectors. This observation would solve the recent discrepancy that the strong effectors remove the cooperativity of oxygen binding in the low-affinity limit, whereas the (1)H NMR spectrum of fully ligated form exhibits the pattern of the R state.
Nagatomo
Shigenori
S
Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Aichi, Japan.
Nagai
Masako
M
Mizutani
Yasuhisa
Y
Yonetani
Takashi
T
Kitagawa
Teizo
T
D001665:Binding Sites; D002248:Carbon Monoxide / Q000032:analysis / Q000737:chemistry*; D006441:Hemoglobin A / Q000032:analysis / Q000737:chemistry*; D006801:Humans; D010100:Oxygen / Q000032:analysis / Q000737:chemistry*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013237:Stereoisomerism
D002248:Carbon Monoxide; D006441:Hemoglobin A; D010100:Oxygen