Suppose that we were interested in determining the strength of the binding of es

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Suppose that we were interested in determining the strength of the binding of estradiol to albumin. We use radiolabeled estradiol (concentration 7. 5 11M) and equilibrate it with various concentrations of bovine serum albumin (B$A) for 30 min at 37C. After equilibration, a small amount of unbound estradiol was removed by solid-phase micro- extraction and measured by liquid scintillation counting. In essence, the scintillation transduces high-energy radioactive emissions to visible light, and a conventional PMT is used to measure the light. In a scintillation experiment, the number of photons from a radiation-induced fluorescence process in an organic dye are measured per unit time and this is related to amount of the radioactive compound by a calibration. If the albumin is present in large excess, we can assume that the unbound albumin concentration [P] is not changed by any interaction. If the initial concentration of estradiol is [X]o and the final concentration of unbound estradiol is [X], the bound estradiol is and the equilibrium constant is which can be rearranged to A graph of [X]o [X] vs. [P] should the refore be linear with slope K. This is a Scatchard plot for binding, and it is commonly used in biochemistry. the quotient here is equal to the counts of the radiolabeled estradiol extracted from solution without albumin divided by counts of labeled estradiol extracted from an equilibrated solution containing estradiol and BSA. For the data given below, prepare a plot of [X]o [X] vs. [P], and find the binding constant K. From the standard deviation of the slope, find the 95% confidence limit for K. What are the units of K?

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