ENTHALPY CHANGE OF THE ALLOSTERIC TRANSITION IN HUMAN HEMOGLOBIN-A

Oxygen equilibria of haemoglobin were analysed using binding isotherms to obtain the intrinsic oxygen association to the haem moities of hae moglobin. Two sets of binding sites in haemoglobin were identified, wh ich were ascribed to the R and T forms of the haems. The average intri nsic association constants, determined as a function of temperature, g ave a heat of oxygenation of 76+/-4 kJ mol(-1) for the haemoglobin tet ramer. A microcalorimetrically determined heat of dissociation of oxyh aemoglobin by dithionate was -267+/-10 kJ mol(-1) (tetramer). From the se results, the heat of allostery of -343+/-14 kJ mol(-1) of the haemo globin tetramer was obtained, yielding an allosteric energy per mole o f salt-bridge of -42+/-4 kJ mol(-1). This results suggest strongly tha t the salt-bridges may be hydrogen bonds. (C) 1997 Elsevier Science B. V.