THE CHLORIDE EFFECT IN THE HUMAN EMBRYONIC HEMOGLOBINS

The interactions of the three human embryonic haemoglobins with chloride ions have been investigated. Each of the three embryonic haemoglobins exhibits a unique pattern of oxygen-affinity-dependence on chloride ion concentration. Human embryonic haemoglobin Portland (zeta(2) gamma(2)) is found to be completely insensitive to chloride ion concentration. Haemoglobin Gower I (zeta(2) gamma(2)) shows a small concentration dependence, whilst haemoglobin cower II (alpha(2) epsilon(2)) exhibits a dependence approaching that of the adult protein. The degree of co-operativity for each protein is essentially chloride concentration independent. The chloride-dependent and -independent components of the alkaline Bohr effects have been measured for each of the embryonic haemoglobins and compared with that of the adult protein. Both the chloride-binding data and the Bohr effect have been analysed in terms of the recently developed allosteric model proposed by Perutz.