A coupling mechanism to inter-relate
regulatory with
haem-haem interactions of haemoglobin
Bennun, A.
The Me2+(Zn2+ or Mg2+)-dependent increase in the oxygenation
of haemoglobin (Hb) is examined theoretically using an overview
in scale of the interface of the a1ß2 dimer of Hb. A
model was developed showing that 2,3 DPG and Me2+ would maintain
a pH-modula¬ted mutually exclusive relationship as ligands
of Hb because they both share a common binding His-ß2143.
A symmetric relationship applies to a2ß1. One atom of
metal, within each dimer, would compete in turn with each
of the haem groups to sequentially dislo¬cate both proximal
histidines during the transition from deoxyHb to oxyHb. Hence,
the pH-modulated reaction path of the multiple equilibrium
of Hb would integrate the inter-actions of either one 2,3
DPG with four histidines for the increase of hindrance effects,
or the interactions of two Me2+ with four haem groups to increase
their affinity for 02. The model predicts that increases in
p02 would increase the affinity of Hb for Me2+ and therefore
for 02, simultaneously decreasing its affinity for 2,3 DPG
and protons.
Biomed. Biochim. Acta, 46, (1987), No. 2/3, 314-319