Revised 2008/05/22
Review equilibria and equilibrium constants. Look also at acid-dissociation constants (Ka), but think about the possibility of using the same equations to describe dissociation of a ligand (substrate, inhibitor, cofactor) from a protein, rather than dissociation of a proton from the conjugate base of an acid. To see what I mean, read on, looking for parallels between
Also, to help you understand the function of heme iron and other biological metal ions, read the chapter on transition-metal complexes in your general chemistry book.
If your course includes a study of the oxygen carrier proteins myoglobin and hemoglobin, you can greatly enhance your understanding of oxygen binding by learning how to derive saturation equations from simple models of ligand binding to proteins.
For the simple dissociation model
start from the dissociation-constant expression with oxygen concentration expressed as partial pressure (the KP for this process), and derive the saturation equation
in which pO2 is the partial pressure of O2, P50 is the partial pressure that gives half saturation (Y = 0.5) of Mb with O2, and Y is the saturation fraction, the fraction of myoglobin molecules with O2 bound at a given pO2. The algebraic definition of Y is
The derivation entails substituting for [MbO2] from the dissociation-constant expression, and simplifying. You also need to show that KP = P50.
Once you have a command of this derivation, you will find it much easier to read the discussions of oxygen transport by myoglobin and its more complex cousin hemoglobin.
(at beginning of first class on hemoglobin function)
Base your work on the derivation described above.
For the all-or-none dissociation model for oxygen and hemoglobin,
prove that
Show all algebraic manipulations, and show clearly that KP is equal to P504
THINK ABOUT THIS: Why doesn't the equation you derived here fit the hemoglogin saturation curve?