Allosteric modulation of oxygen binding to the three human embryonic haemoglobins.

Plasmid based yeast expression systems have been developed for the high-level expression of the three human embryonic haemoglobins Gower I (zeta 2 epsilon 2), Gower II (alpha 2 epsilon 2) and Portland (zeta 2 gamma 2). Physiochemical characterization of the three product haemoglobins show them to be in the 'native' state. Oxygen-binding studies show that, under what are usually considered physiological conditions, each of the embryonic haemoglobins shows a high oxygen affinity, coupled to a high degree of co-operativity. Allosteric modulation of the oxygen-binding properties of the three haemoglobins in response to organic phosphates and protons has been investigated. The various responses exhibited by the three haemoglobins are rationalized in terms of their amino acid sequences.