Is Ligand Binding Cooperative and How Many Binding Sites Does the Protein Have?

[kittybobo1]

Homework Statement

The binding of a ligand B to a protein is studied. The protein concentration it 10^-3 M. The amounts bound,b, for each added is given as the following:

(M) (b)(M)
.001 5*10^-6
.002 3.3*10^-3
.005 3.78*10^-3
.007 4.72*10^-3
.01 4.95*10^-3
.02 5*10^-3
.05 5*10^-3

Find if it is cooperative, the number of binding sites, and K_d

Homework Equations

The hills equation can be expressed as log Y/(1-Y) =n log [A] - log K_d

The Attempt at a Solution

So the y intercept is - log K_d and the slope is n when you plot the left side in respect to log [A]. Y is the fractions filled, so I think it would be (b)/(5*10^-3). But, plotting the graph.. it seems a little screwy.. the plot goes from slope of 10.9 to .5 then to ~5.. The graph is shown here.

 

[epenguin]

So the y intercept is - log K_d and the slope is n when you plot the left side in respect to log [A]. Y is the fractions filled, so I think it would be (b)/(5*10^-3). But, plotting the graph.. it seems a little screwy.. the plot goes from slope of 10.9 to .5 then to ~5.. The graph is shown here.

If it were I could probably help, but I can't see it.

Possible sources of confusion:
1) [A] in your equation is concentration of free A in solution, did you calculate that?;
2) That's enough possible sources of confusion till I see your graph.

And to make it easier for us and yourself put also the free A in a table with the other parameters.