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Unformatted text preview: between total binding and nonspecific binding.
d) Using the specific binding curve below, determine the Kd of TGFß57 for high-affinity
receptors. Also, find the total number of receptors per cell.
*** NOTE: y-axis label: [I125] TGFb-57 Bound (molecules per cell) Answer: The Kd is determined by finding the concentration of TGFß57 at half-maximal
binding. Kd= 10nM. The total number of receptors per cell is 19,000.
e) You’d now like to determine the sensitivity of these cells to TGFß57. You know that the Kd
for binding TGFß57 to its receptor is about 1X10-8 and you know there are a total of 19,000
receptors per cell. You have previously determined that only 13% of the 19,000 receptors must
be bound to obtain the maximal cellular response. Determine the TGFß57 concentration needed
to induce the maximal response. What would be the concentration of TGFß57 required to obtain
maximal response if there were only 5000 receptors per cell, what is the fold difference 7.06 Spring 2004 PS 2 KEY 3 of 7 compared to the normal concerntration you just calculated, and would this make the cell more or
less sensitive to TGFß57? Why might a cell want to regulate the number of receptors to a given
Answer: To calculate the concentration of TGFß57 to induce maximal response, you use
the equation [L] = Kd/(RT/[RL])-1. [RL] is the number of TGFß57-occupied receptors
needed to induce maximal response—which is 13% of 19,000. Plugging all the values in to
the equation gives you [TGFß57] = 1X10-9M. If the total number of receptors was reduced
to 5000, the [RL] would still be 2470, then [TGFß57] = 5X10-9M—a 5-fold increase in the Kd
of TGFß57. This decrease makes the cell less sensitive to TGFß57 because there needs to be
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