[nlb149]

1. Write the equations which describe the relative populations of the states of a
protein in which linkage of ligand binding is coupled to a conformational change
in a protein which results in a change in ligand affinity. Assume that there are two
independent, identical binding sites on the protein, and therefore there are six
states:
R <->    T
|          |
R.L <-> T.L
|            |
R.L2 <-> T.L2
(the vertical bars should be read as double arrows pointing up and down and all
reactions are reversible). The intrinsic equilibrium constant for conversion of R to
T is K (=[T]/[R]). The dissociation constants for L binding to T and R are kT and
kR, respectively. Assume that the dissociation constants for binding of the
second ligand to T and R are the same as for the first binding reaction.

2. Write an expression for the binding density in terms of the three equilibrium
constants for the elementary reactions and the free ligand concentration.

Okay so I got the answers for 1 to be:
Q = 1 + K + Kr[L] + (K * Kt[L]) + (Kr[L] * Kr[L]) + (K * Kt[L] * Kt[L])
Pr = 1 / Q
Pt = K / Q
Prl = Kr[L] / Q
Ptl = (K * Kt[L]) / Q
Prl2 = (Kr[L] * Kr[L]) /Q
Ptl2 = (K * Kt[L] * Kt[L]) / Q

However, I'm not sure what equation for the binding density I'm suppose to use for part 2