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.