Oxyhemoglobin differences from

Occasionally small amounts (less than 5 percent of the total protein) of material with mobilities different from that of either kind of hemoglobin were observed in these uncrystallized hemoglobin preparations. According to the observations of Stern, Reiner, and Silber (f2) a small amount of a component with a mobility smaller than that of oxyhemoglobin is present in human erythrocyte hemolyzates. 

The absorption spectrum of oxyhemoglobin is markedly different from that of hemoglobin. The former has two sharp well-defined absorption bands between D and E, while the latter has only one. Such differences in the absorption spectra cannot be explained on the grounds of a difference in state, nor in the degree of dispersion of the hemoglobin. Rather it indicates a change in the chemical composition of the two substances. 

Fig. 19.7 Stercoview of superimposed heme environments in oxyhemoglobin and oxymyoglobin. Solid lines denote HbO and dashed lines MbOj. Note the difference in the Fe—01—D2 bond angles and the presumed hydrogen bond (dotted line) to the histidine (His E7). [From Shaanan, B. Nature (LonJvn) 982,296, 683. Reproduced with permission.]...

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. 

COHb is quite stable and its concentration does not change over a long period (up to 6 months) if the blood sample is stored in the dark and under sterile conditions. Blood levels of COHb are not expected to exceed 5% at ambient levels of CO. IPCS (1999) focuses on methods which can accurately measure COHb below 10%. A method which simply requires finger-prick blood is convenient for mass screening and is described in detail by Commins and Lawther (1965) in this method, the sample is diluted in ammonia solution, which is divided into two parts from one of these, CO is displaced by oxygen and the COHb containing part is placed in the sample beam of a spectrophotometer so that the instra-ment records the difference between the absorbance of COHb and oxyhemoglobin. 

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