Kinetik der Dissoziation von Alkylisocyanidkomplexen monomerer und oligomerer Hamoglobine

The dissociation of isocyanide complexes of human adult and fetal haemoglobin, of the Hb of carp and cheironomus, and of the horse myoglobin has been investigated by means of replacing the R-NC ligand by CO. Furthermore the dissociation of Hb-A complexes induced by dilution has been studied. Ligand replacement on Mb occurs homogeneously. Associated Hb however exhibit biphasic reactions. This behaviour is believed to depend on subunit differences in reactivity. No ligand specifity could be observed. The dissociation rate constant k decreases in the sequence Mb > Hb-F ≅ Hb-A ≅ carp Hb > cheironomus Hb. The only small variation of k confirms that the species differences in the equilibrium constant K are mainly attributable to the variation of the respective association velocity constants k′. Compared with Hb-A, carp- and especially cheironomus-Hb exhibit an enhanced decrease of k with increased ligand size, this being probably due to interactions between apolar protein side chains in the haem pocket and the respective ligand. Additional dilution relaxation experiments show that the dissociation rate constant k decreases with increasing percentage R-NC-saturation of Hb; this confirms the dissociation reaction to be the kinetic basis of haem haem interaction. In the presence of allosteric effectors (inositole hexaphosphate) again the decreased equilibrium constants of the R-NC complexes are mainly due to lower k' values, while k varies to a minor extent.