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Loss of allosteric behaviour in recombinant hemoglobin α 2 β 2 9 r )F8)His→Ala: Restoration upon addition of strong effectors
Author(s) -
Dumoulin A.,
Kiger L.,
Jiang R.,
Baudin V.,
Vasseur C.,
Sligar S.G.,
Marden M.C.,
Pagnier J.,
Poyart C.
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)01069-q
Subject(s) - allosteric regulation , cooperativity , chemistry , histidine , cooperative binding , ligand (biochemistry) , heme , stereochemistry , kinetics , alanine , hemoglobin , crystallography , binding site , receptor , biochemistry , amino acid , enzyme , physics , quantum mechanics
In the stereochemical model proposed by Perutz [1], the Fe‐His(F8) bond plays a significant role in the allosteric transition in hemoglobin and the resulting cooperativity in ligand binding. When this bond is ruptured, there is a loss in the transmission of the information concerning ligand binding; examples are Hb(NO) 4 in the presence of inositol hexakisphosphate (IHP), or nickel substituted Hb hybrids which, despite being liganded, exhibit deoxy‐like properties. To study the effects of the loss of the iron proximal histidine bond, we have engineered the α 2 β 2 (F8)H92A recombinant Hb. The replacement of the highly conserved proximal histidine F8 residue by an alanine results in a low affinity for the heme group and a loss of the allosteric properties; kinetics of CO recombination after photodissociation show only the rapid bimolecular phase, characteristic of the high affinity R‐state. However, a significant amount of deoxy (T‐state) kinetics are observed after addition of external effectors such as IHP. The iron‐histidine bond is apparently crucial for the heme‐heme interaction, but the allosteric equilibrium may still be influenced by external constraints.