Subunit Dissociation of the Unstable Hemoglobin Bibba (α2136 ro (H19)β2)

Cyanferrihemoglobin Bibba (α2136 pro(H19)β2) was found by sedimentation velocity and viscosity measurements to be extensively dissociated into dimers in dilute salt solution at neutral pH. The dissociation constant in 0.1 m NaCl, at pH 7.2 and 25°, is about 500 x 10-6 m. The deoxy form is likely more associated than the cyanferri derivative. The cyanferri derivative of this hemoglobin variant is relatively stable in buffers of neutral and alkaline pH and low ionic strength. At pH 10.7, hemoglobins Bibba and A are both primarily dimers. At this pH, hemoglobin A maintains a compact, globular structure, while hemoglobin Bibba undergoes some type of molecular expansion or unfolding. At pH 4.9, the highly dissociated hemoglobin Bibba is unstable and precipitates readily.