Data in the table come from a student experiment to measure the binding constant of the radioactively labeled hormone estradiol (X) to the protein, bovine serum albumin (P). Estradiol (7.5 nM) was equilibrated with various concentrations of albumin for 30 min at 37C. A small fraction of unbound estradiol was removed by solid-phase microextraction (Section 23-4) and measured by liquid scintillation counting. Albumin is present in large excess, so its concentration in any given solution is essentially equal to its initial concentration in that solution. Call the initial concentration of estradiol [X]0 and the final concentration of unbound estradiol [X]. Then bound estradiol is [X]₀ - [X] and the equilibrium constant is

which you can rearrange to

A graph of [X]₀/[X] versus [P] should be a straight line with a slope of K. The quotient [X]0/[X] is equal to the counts of radioactive estradiol extracted from a solution without albumin divided by the counts of estradiol extracted from a solution with estradiol.

(a) Prepare a graph of [X]0/[X] versus [P] and find K. From the standard deviation of the slope, find the 95% confidence interval for K.

(b) What fraction of estradiol is bound to albumin at the first and last points?

Transcribed Image Text:

[PX] [X], - [X] X + P= PX K = %3D [X][P] [X][P]