Biochimie & Biochimie Analytique

Abstrait

Equation of State for O₂-Binding by Hemoglobin in Human Red Blood Cells

Francis Knowles*, Douglas Magde

O₂-Equilibrium binding data of hemoglobin in whole blood under standard conditions was fitted to an equation of state comprised of three unknown quantities: K_α, the equilibrium constant for binding O₂ by equivalent low affinity α-chains; K_Δ, a dimensionless equilibrium constant describing the change between low-and high-affinity structures of hemoglobin, ^Tstate and ^Rstate; K_β, the equilibrium constant for binding O₂ by equivalent high affinity β-chains. Values of the unknown quantities at pH 7.4 and 37°C are: K_α=15,090 L/mol; K_Δ=0.0260; K_β=393,900 L/mol. A graph of predicted versus observed values of fractional saturation, F, is linear: F_PRE=0.9998 F_OBS=0.0005, R²=0.9997. The Perutz/Adair equation of state is defined as such insofar as all aspects of the stereo chemical are imposed on the earlier sequential binding model of Adair. The Perutz/Adair equation of state is general, describing: (i) the CO equilibrium binding curve of whole blood under standard conditions, K_α=4.27 × 10⁶ L/mol, K_Δ=0.05741, and K_β=99.1 × 10⁶ L/mol; (ii) the O₂-equilibrium binding curve of purified hemoglobin in 0.100 M NaCl, 0.050 M BisTris, pH 7, 20°C, K_α=5.34 × 10⁴ L/mol, K_Δ=0.03252, and K_β=1.81 × 10⁶ L/mol.