Quaternary Structures of Intermediately Ligated Human Hemoglobin A and Influences from Strong Allosteric Effectors: Resonance Raman Investigation

• Published in: Biophysical journal 2005-08, Vol.89 (2), p.1203-1213
• Main Authors: Nagatomo, Shigenori, Nagai, Masako, Mizutani, Yasuhisa, Yonetani, Takashi, Kitagawa, Teizo
• Format: Article
• Language: English
• Subjects: Binding Sites; Carbon Monoxide - analysis; Carbon Monoxide - chemistry; Crystallography; Hemoglobin; Hemoglobin A - analysis; Hemoglobin A - chemistry; Humans; Oxygen; Oxygen - analysis; Oxygen - chemistry; Phosphates; Protein Binding; Protein Structure, Quaternary; Proteins; Spectrum Analysis, Raman - methods; Stereoisomerism
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.104.049775

The Fe-histidine stretching ( ν 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 ν 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 ν 4 band measured in the same experiment. The α1- β2 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 1H NMR spectrum of fully ligated form exhibits the pattern of the R state.