DIFFERENT STRUCTURAL EFFECTS OF ALLOSTERIC MODULATORS ON SUBUNITS OF TETRAMERIC FERROUS NITROSYLATED HUMAN HEMOGLOBIN - AN EPR SPECTROSCOPIC STUDY

The X-band EPR spectroscopic features of the ferrous nitrosylated deri vative of alpha(Fe)(2) beta(Co)(2) and of alpha(Co)(2) beta(Fe)(2) met al hybrids of human hemoglobin (Hb) have been investigated at pH 7.0 a nd analyzed in parallel with those of the native nitrosylated tetramer (HbNO). The effect of 2,3-biphosphoglycerate (BPG), inositol hexakisp hosphate (IHP) and bezafibrate (BZF) has been investigated in order to understand the perturbations induced on alpha and beta subunits in th e tetramer by the binding of allosteric effecters. A large perturbatio n is observed in both subunits upon BZF binding, while in the case of IHP only alpha-chains are affected; on the other hand, BPG leaves both chains essentially unperturbed. Thus, different binding modes of allo steric effecters to HbNO may occur, and the simultaneous addition of t wo effector molecules, namely BPG and BZF or IHP and BZF to HbNO, brin gs about different alterations of the X-band EPR spectroscopic propert ies. This behavior indicates that the intramolecular communication pat hway(s) between the heme and the binding pockets of the heterotropic l igands (i.e., IHP and BZF, or BPG and BZF) are different, leading to d istinct structural perturbations.