8. (6 pts) You wish to determine the hormone-binding specificity of a newly iden

Question

8. (6 pts) You wish to determine the hormone-binding specificity of a newly identified membrane receptor. Three different hormones, X, Y, and Z, were mixed with the receptor in separate experiments, and the percentage of binding capacity of the receptor was determined as a function of hormone concentration, as shown in graph A. wS 10 10* 10* 10 You next wish to determine whether the hormone-receptor complex stimulates the adenylate cyclase cascade. To do so, you measure adenylate cyclase activity as a function of hormone concentration, as shown in graph B (b) Does the hormone-receptor complex have the ability to enhance adenylate cyclase activity? Explain.

Explanation / Answer

From the given figure, the below values are derived.

96% Vmax - X hormone

90% of max – Y hormone

82% of max – Z hormone

At ½ max = hormone concentration is Km of the reaction

So, Km of X hormone is 48% of max from the graph

At 48% of Vmax, hormone conc. is 10^-7M

At 45% of Vmax, Y hormone conc. is 10^-5.5M

At 41% of Vmax, Z hormone conc. is 10^-3M

As binding affinity is high at low Km value,

X hormone is considered to be having higher binding affinity with the receptor than the other two

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