1. Many drugs act as antagonists of transmembrane receptors. If a small-molecule

Question

1. Many drugs act as antagonists of transmembrane receptors. If a small-molecule G protein coupled receptor antagonist inhibits its target by 50% at a concentration of 2 x 10^-8 M, what concentration would be needed in the bloodstream to inhibit receptor activity by 99%? If the compound has a molecular mass of 500 daltons, how much of the drug would be needed to achieve this concentration in the bloodstream (assume that all of the drug enters the bloodstream, which as a volume of 5 liters)?

2. Receptors that have intrinsic or associated kinase activity depend on dimerization and/or clustering in order to transmit downstream signals. A key step in activating the associated kinase activity is usually input-dependent phosphorylation on the kinase activation loop. However, there are a few receptor-associated kinases that do not require activation-loop phosphorylation for signaling. How might it be possible to transmit signals without activation-loop phosphorylation? Similarly, consider the role of cellular phosphatase activity. In what ways would a much higher or lower phosphatase activity affect the signaling properties of the receptor?

Explanation / Answer

1. Part 1

According to question,

50% coupled receptor can be inhibited at concentration=2 x 10^-8 M

Therefore, 99% coupled receptor can be inhibited at concentration= [{(2 x 10^-8 M)/50} x 99]=3.96 x 10^-8 M

Part 2

Molecular mass (Also called Formula Weight)= 500 Da= (500 x 1) g/mol= 500 g/mol

Volume= 5 L

Desired concentration= 3.96 x 10^-8 M (From 1st part)

We know that, Mass (g) = Concentration (mol/L) x Volume (L) x Formula Weight (g/mol)

Therefore, drug required in the bloodstream (g)= (3.96 x 10^-8 M) x 5 L x 500 g/mol= 0.0099 g

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