Mechanical Instability of the Oxy-form of Sickle Haemoglobin

Abstract

MUCH attention has been given to the molecular aspects of the deoxy form of sickle haemoglobin (Hb S) because sickling occurs with Hb S in the deoxygenated state. The oxy form of Hb S, on the other hand, is believed to be similar to normal adult haemoglobin (Hb A) with respect to solubility^1,2, X-ray diffraction pattern³, oxygen binding⁴ and other properties. During determination of oxygen equilibrium curves of Hb S, we noticed that a solution of oxyhaemoglobin S became turbid very easily when it was stirred or mixed. The turbidity was found to be due to protein which was denatured by the mechanical force involved and/or by foaming. Oxyhaemoglobin S denatured more quickly than oxyhaemoglobin A by mixing, stirring or sonication. The rate of denaturation was dependent on the oxygen concentration in the medium, suggesting that an oxidative process was involved. As demonstration of denaturation requires only a few drops of blood, water and shaking, this property can be used as a simple clinical test for the presence of Hb S.