Oxygen fractional saturation

If Y is defined as the fractional saturation of myoglobin with Og, that is, the fraction of myoglobin molecules having an oxygen molecule bound, then... 

Figure 7.1 Fractional saturation Yv of tetramer with molecular oxygen calculated with the binding constants in equations 7.1-3 to 7.1-6 (see Problem 7.3).

Calculate the fractional saturation YT of the tetramer of human hemoglobin with molecular oxygen using the equilibrium constants determined by Mills, Johnson, and Akers (1976) at 21.5 °C, 1 bar, pH 7.4, [Cl"] = 0.2 M and 0.2 M ionic strength. Make the calculation with the Adair equation and also by using the binding polymomial YT. 

Suppose we run oxygen at 750 torr through a vaporizer in such a manner that the oxygen becomes saturated with enflurane. In this case, the partial pressure of enflurane in the effluent will equal the vapor pressure of enflurane. The pressure of the effluent gas remains at 750 torr, but the effluent gas is now saturated with enflurane. The mole fraction of enflurane is given by Dalton s law ... 

Fig. 46. 250-MHz ferric hyperfine-shifted proton resonances of the abnormal p chains of 15% Hb M Milwaukee (p67Val — Glu, a2p2) as a function of oxygenation in 0.1 M Bis—Tris in D20 at pH 6.6 and 30°C. The proton chemical shifts are referenced to HDO. The range of the fractional saturation (y) was based on P50 = 5 torr or P5 = 10 torr. [Adapted from Fung et al. (1977)].

At specified concentration of molecular oxygen, the five forms of hemoglobin are pseudoisomers, and they have the same further transformed Gibbs energy of formation at equilibrium. The further transformed thermodynamic properties of the tetramer can be calculated from experimental measurements of the fractional saturation, but in order to interpret experimental data, it is necessary to provide for the partial dissociation of tetramer 02 Bz into dimers a/3 (3). Seven apparent equilibrium constants are required to describe experimental data, and it is shown that all seven can be determined using limiting forms (4). 

R. A. Alberty, Determination of the seven apparent equilibrium constants for the binding of oxygen by hemoglobin from measured fractional saturations, Biophys. Chem. 63,119-132 (1997). 

So that we can deal with measurable parameters. Equation (7.2) needs to be modified by the introduction of two terms, Y and P50. Y is defined as the fractional saturation of myoglobin, e.g., when Y = 0.3, 30% of the available sites on the myoglobin are occupied by oxygen. Thus,... 

Figure 7.30 Modeling oxygen binding with the concerted model. The fractional saturation (V) as a function pO. t = 9000, c "" 0.014, and = 2.5 torr. The fraction of molecules in the T state with zero, one. and two oxygen molecules bound (Tq, T. and Tj) and the fraction of molecules in the R state with two. three, and four oxygen molecules bound R2, R3. and R4 are shown. The fractions of molecules in other forms are too low to be shown.

Another way to look at it is to calculate the fraction of myoglobin that is in the oxygenated form, or the fractional saturation of myoglobin ... 

Partial pressure of oxygen calculated from the space average fractional saturation of blood, torr Radius of fetal capillary, cm Radius of maternal channel, cm Radius of tissue cylinder, cm Dimensionless radial distance Variable radius, cm Time, sec... 

Figure 3. Oscilloscope trace of a temperature-jump experiment on Octopus hemocyanin reacting with oxygen. Potassium phosphate buffer, 0.2M, pH 7, and 20 C (before the jump). Discharge 30 kv yielding a temperature increase of 4 to 5 C. Protein concentration = 4.5 X 10 binding equivalent L fractional saturation with oxygen = 0.53 free oxygen concentration = 3.4 X lOr M. Sweep time = 100 fxsec per large screen division observation wavelength = 348 nm (24).

FIG, 2. Fractional saturation curves of ferrohemoglobin with oxygen, ethyl isoeyanide, Isopropyl isoeyanide, and tertiary butyl isoeyanide at 25° C and pH 6.8. The dashed curve n = 1 corresponds to no heme-heme interaction, and the dashed curve n = 2 to strong interactions between the hemes in pairs. Ordinates, fractional saturation 0 to 1 abscissae, log of concentration of unbound oxygen or Isoeyanide -5.1 to -1.0. 

Fig. 4.9 The variation of the fractional saturation of myoglobin and hemoglobin molecules with the partial pressure of oxygen. The different shapes of the curves account for the different biological functions of the two proteins.

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