Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

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QUANTITATIVE Pure agony. Agonists are drugs that bind to receptors and activate them, like their normal ligands. Suppose you work for a pharmaceutical corporation, and you are testing the receptor affinity of a new preparation of phenylephrine, which is primarily used as a selective agonist of 1 -adrenergic receptors in over-the-counter decongestants. Physiological ligands for 1 -adrenergic receptors are epinephrine and norepinephrine. Assume that phenylephrine can saturate the receptors in this assay to the same extent as its normal ligands if enough phenylephrine is added (that is, phenylephrine can bind nearly 100% of the receptors if enough is added). You measure the K d for epinephrine, norepinephrine, and phenylephrine and find it is 63, 196, and 239 n M , respectively. Draw a graph that represents the change in percent of 1 -adrenergic receptors bound versus concentration for each ligand. Be sure to label your axes and the curve for each ligand. Indicate the K d for each on your graph.