Deoxyhemoglobin differences from

Oxyhemoglobin has a different quaternary structure from deoxyhemoglobin. As 02 binds to the Fe2+ it distorts the heme group and moves the proximal histidine. This in turn moves helix F and alters the interactions between the four subunits. 

Figure 3. Resonance Raman spectra of human deoxyhemoglobin in the T and R structures with difference spectrum, showing the shifts to lower frequency on transition from T to R (34).

Succinyl-L-tryptophan-L-tryptophan (STT, 8) and p-bromobenzyl-oxyacetic acid (BBA, 9) also bind to deoxyhemoglobin at several sites. In the case of STT, four different sites are involved. The major portion of binding in the case comes from hydrophobic contacts in which 21 molecules of water are displaced. Each STT is bound to one a. subunit by three hydrogen bonds and several van der Waals interactions (Figure 18). STT binds to the protein with a Kd of 3.0 mM. BBA is held in place by a salt bridge between its carboxylate and Lys-40. There are also van der Waals contacts between its bromine and the aliphatic protion of the side chain of Glu-30 (Figure 19). 

Earlier reports focused on the use of optical absorption properties of tissues for clinical applications (Wilson and Jacques, 1990). An example is blood oximetry, which is widely used clinically to monitor continuously blood oxygenation with the help of an optical fiber probe as described in the previous section. In this method the diffuse reflectance also collected by the fiber is analyzed based on the differences in the absorption bands of oxy and deoxyhemoglobins. Diffuse reflectance from the skin can be used to monitor changes induced, for example, by the UV radiation. Endoscopic reflectance spectroscopy from mucosa of the gastrointestinal tract has been used to determine blood content and oxygenation (Leung et al, 1989). 

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