Relationship between structural changes of protein and function of abnormal hemoglobin.

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X-ray crystallographic studies have shown that the deoxy and liganded forms of hemoglobin (Hb) poseesee two distinct quaternary structures named T-and R-states, respectively. Cooperative oxygenation to Hb has been explained in terms of a reversible transition between the two quaternary structures upon partial ligation to the four hemes. Environmental changes of tyrosine (Tyr) and tryptophan (Trp) residues of Hb upon its T-to-R transition of quaternary structure was ivestigated with ultraviolet resonance Raman (UVRR) spectroscopy and circular dichroism (CD) . To characterize the spectral change of Trp beta37 at alpha_1beta_2 interface due to the quaternary structure transition, the UVRR spectra of Hb A were compared with the corresponding spectra of Hb Hirose in which Trp beta37 is replaced by serine (Ser) . Difference spectrum between deoxyHb A and deoxyHb Hirose gave rise to only Trp RR bands, which were reasonably ascribed to Trp beta37 in deoxyHb A.Comparison of the Hb A-Hb Hirose difference spectra in the oxy and deoxy states revealed that the oxygenation-induced changes of Trp RR bands arose mostly from Trp beta37 and the remaining minor part from Trp beta15, demonstrating that Trp beta37 plays a pivotal role in the quaternary structural change in Hb A.