Hemoglobin disaggregation

Figure 6. The fraction of oligomeric channels open as a function of the surface charge density (in charges per 100 nm2). The equilibrium constant for the channel-opening reaction is assumed to be equal to that of hemoglobin disaggregation, which is also a function of the charge.

To test the quantitative predictions of the model, we measured the disaggregation of the hemoglobin tetramer by the increase in osmotic pressure with pH (5). When the pressure is compared to that observed in solutions of bovine serum albumin (BSA a protein of comparable molecular weight that does not disaggregate), we can ascribe the difference in pressure to disaggregation. In the titration of both protein solutions, the minimum pressure occurs at the isoelectric point (IEP), which is 6.82 0.06 for hemoglobin at 25.0 °C. 

Figure 3. The logarithm of the disaggregation equilibrium constant, Kd, as a function of the charge, Q, on the hemoglobin molecule. The points and dashed line are experimental, while the solid line is based on the surface free energy calculation. (Reproduced with permission from Bioelectrochem. Bioenerg.)...

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