What is the fractional saturation of O2 for hemoglobin at 39

What is the fractional saturation of O2 for hemoglobin at 39.65 torr? Assume that n=3 and a P50 of 26 torr.

Solution

Answer- To calculate fractional saturation of oxygen for hemoglobin we can use Hills equation which is based on ligand protein saturation

Here oxygen is ligand and hemoglobin is protein

Concentration of oxygen is shown as partially pressure

Po2 = 39.65 torr

n =no. Of subunits the more cooperative the binding is

In our case it is 3 which is close to the maximum value 4 ( because hemoglobin can bind with 4 molecules of oxygen)

And the KD value (apperent dissociation constant) is equal to P50

Where half the ligand bind with protein.

According to Hills equation

Y O2=[L]n/KD+[L]n

( Note- n is the power of [L]

Yo2=[po2]n/P50+[po2]n

Yo2=[39.65]3/26+[39.65]3

=0.0999

By rearranging the equation

Log Yo2/1-Yo2=nlog[Po2] -log [P50]

Log 0.0999/1-0.0999=3log(39.65) -log(26)

Log 0=3 x 1.598 -1.414

Log 0=4.794-1.414

Log 0=3.38