title: A kinetic description of dioxygen motion within alpha- and beta-subunits of human hemoglobin in the R-state: geminate and bimolecular stages of the oxygenation reaction.
abstract: Laser flash photolysis technique is used to study human hemoglobin (HbA) oxygenation. Monomolecular geminate oxygenation of triliganded R-state HbA molecules is described by a function of three exponentials. Geminate oxygenation of the alpha-subunit within R-state HbA is characterized by two components with time constants of 0.14 and 1 ns, while geminate oxygenation of the beta-subunit within HbA is characterized by two components with time constants of 1 and approximately 30 ns. Bimolecular oxygenation of triliganded R-state HbA molecules is described by a biexponential law. Two observed rate constants are assigned to oxygenation of the alpha- and beta-subunit within HbA. The bimolecular association rate constants for O(2) rebinding with the alpha- and beta-subunit within triliganded R-state HbA are k(alpha) = 18.8 +/- 1.3 (microM x s)(-1) and k(beta) = 52 +/- 4 (microM x s)(-1), respectively. The apparent quantum yields of photodissociation of the beta- and alpha-subunit within completely oxygenated R-state HbA differ from each other by a factor of 3.6 and are equal to 0.041 +/- 0.004 and 0.0114 +/- 0.0012, respectively. The apparent quantum yield of photodissociation of completely oxygenated R-state HbA is equal to 0.026 +/- 0.003.
authors.affiliation: Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skaryna Ave., Minsk 220072, Belarus.
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Lepeshkevich
authors.forename: Jerzy
authors.initials: J
authors.lastname: Karpiuk
authors.forename: Igor V
authors.initials: IV
authors.lastname: Sazanovich
authors.forename: Boris M
authors.initials: BM
authors.lastname: Dzhagarov
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D005914:Globins / Q000737:chemistry*; D006441:Hemoglobin A / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D036103:Nanotechnology / Q000379:methods; D009569:Nitric Oxide / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D010782:Photolysis; D021122:Protein Subunits / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D008024:Ligands; D021122:Protein Subunits; D009569:Nitric Oxide; D002248:Carbon Monoxide; D005914:Globins; D006441:Hemoglobin A; D010100:Oxygen