Biology Reference
In-Depth Information
47
Figure 2.7.
Hill's plot for the experimental results of Roughton
et al.
with error bars of 0.5% for all ten measurements.
TWO-CONSTANT MODEL
Pauling proposed two theoretical models for hemoglobin saturation in 1935,
both with two constants. Only his tetrahedral model will be discussed here.
In this case, he assumed that the two -subunits and two are
arranged in a tetrahedral configuration, as verified by X-ray diffraction
studies years later. Different numbers of oxygen molecules, zero to four,
would bind to these four subunits. On the addition of an oxygen molecule to
the heme, he assumed that there would be a free energy change of RT ln K'
which defined the constant K', where R is a universal constant and T the
absolute temperature. He further assumed that the stabilizing energy
associated with two neighboring oxygenated hemes could be denoted by RT
ln which defined the constant If we denote the relative amount of
deoxy-hemoglobin as 1, then the relative amounts of hemoglobin with one
to four oxygen molecules would be:
