ALLOSTERIC MODULATION OF OXYGEN-BINDING TO THE 3 HUMAN EMBRYONIC HEMOGLOBINS

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)). Physicochemical 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 phosphate and protons has been investigated. The various responses exhibited by the three haemoglobins are rationalized in terms of their amino acid sequences.