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

Plasmid based yeast expression systems have been developed for the hig h-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 h aemoglobins show them to be in the 'native' state. Oxygen-binding stud ies show that, under what are usually considered physiological conditi ons, each of the embryonic haemoglobins shows a high oxygen affinity, coupled to a high degree of co-operativity. Allosteric modulation of t he oxygen-binding properties of the three haemoglobins in response to organic phosphate and protons has been investigated. The various respo nses exhibited by the three haemoglobins are rationalized in terms of their amino acid sequences.