Flash photolytic studies of carbon monoxide binding to the ferrous chains of [Mn(II),Fe(II)] hybrid hemoglobins: kinetic mechanism for the early stages of hemoglobin ligation.
Flash photolysis is employed to investigate the kinetics of CO recombination to the ferrous chains of [Mn(II),Fe(II)] hemoglobin (Hb) hybrids. At low pH (6.6), Hb remains predominantly in the T quaternary state for the first two CO ligation steps, when binding to either the alpha chains or beta chains. At elevated pH, CO binding to the alpha chains produces a larger degree of T to R conversion than binding to the beta chains, in support of earlier equilibrium measurements. This study provides the full pH dependence of the CO binding rate constants for both alpha- and beta-Fe chains within the T state and at elevated values of pH gives the R-state rate constants for the monoliganded analogues. The data can be analyzed within the context of a two-state model for Hb cooperativity, but they give clear evidence for slow quaternary structure interconversion at the monoliganded level.
D002248:Carbon Monoxide / Q000097:blood*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008433:Mathematics; D008961:Models, Structural; D010782:Photolysis; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization
D006454:Hemoglobins; D046911:Macromolecular Substances; C042513:manganese-iron hybrid hemoglobin; D002248:Carbon Monoxide