Surface activity of hemoglobin S and other human hemoglobin variants

The kinetics of surface pressure change (deltapi vs. t isotherms) were determined for several single point mutations of the human hemoglobin system. It was observed that hemoglobin S and hemoglobin CHarlem (both containing beta6 Glu leads to Val substitutions) have a specific behavior at the water-air interface: their extent of surface pressure change is larger than for hemoglobin A, hemoglobin C and hemoglobin Korle Bu (beta73 Asp leads to Asn). In addition, hemoglobin S seems to occupy a larger area per molecule than hemoglobin A. The conformational requirements for this property, in addition to the beta6 Val substitution, appear to be the liganded state of the betas chain in the tetramer. Electrostatic, hydrogen bonding and hydrophobic interactions are involved in determining the surface activity of a hemoglobin molecule. The differences between the surface activity of oxyhemoglobin S and oxyhemoglobin A could be the basis for their differences in mechanical precipitability, although other factors may play a role.