Reference no: EM131732769

Problem 3. Competition experiment.

0.5 nM radioligand L* is bound to 1 ml samples of the same membrane samples used in the above experiments in the presence or absence of varying amounts of either compound A or compound B. After establishing equilibrium, the following counts were bound to the membranes (after subtracting nonspecific binding):

Concentration A (nM)	CPM bound with A	Concentration B (nM)	CPM bound with B
0	73001	0	73001
0.05	72100	0.05	66365
0.1	71221	0.1	60835
0.3	67908	0.3	45626
0.5	64890	0.5	36501
1	58401	1	24334
3	41715	3	10429
5	32445	5	6636
10	20858	10	3476
30	8588	30	1197
100	2808	100	363
300	961	300	121

a) Which compound, A or B, is more a more potent displacer of the radioligand? Justify your answer why you think so.

b) Plot the fractional binding on a semilog plot and estimate the IC50s for both A and B.

c) Plot the results on a logit-log plot (pseudo-Hill plot) and determine the IC50s for both compounds A and B. Use these values for the next step. How close are the computed values to your estimate in part b?

d) Use the Cheng-Prusoff equation and the value of Kd for ligand L determined by the Scatchard plot in question 2 to calculate the Ki values for compounds A and B.