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Chapter 25: Problem 3

Suppose at certain specific metabolite concentrations in vivo the cyclic cascade regulating \(E\). coli glutamine synthetase has reached a dynamic equilibrium where the average state of GS adenylylation is poised at \(n=6 .\) Predict what change in \(n\) will occur if: a. [ATP] increases. b. \(P_{11} / P_{110}\) increases. c. \([\alpha-\mathrm{KG}] /[\mathrm{Gln}]\) increases. d. \(\left[P_{i}\right]\) decreases.

Short Answer

Expert verified
a. Increase in [ATP] leads to an increase in n. b. Increase in \(P_{11} / P_{110}\) also leads to an increase in n. c. Increase in \([\alpha-\mathrm{KG}] /[\mathrm{Gln}]\) leads to a decrease in n. d. Decrease in \(P_{i}\) results in an increase in n.

Step by step solution

01

Impact of ATP concentration change

Increase in ATP concentration promotes adenylylation of GS. For \(E\). coli GS, each adenylylation leads to an increase in the n value by 1. Therefore, an increase in ATP concentration would result in an increase in the n value.
02

Impact of \(P_{11}\) and \(P_{110}\) ratio change

An increase in the ratio \(P_{11} / P_{110}\) implies that there is more UTase/UR in the active, uridylylated state (P 110). This state promotes adenylylation of GS, hence with such an increase, the value of n would also increase.
03

Impact of \([\alpha-\mathrm{KG}] /[\mathrm{Gln}]\) ratio change

An increase in the \([\alpha-\mathrm{KG}] /[\mathrm{Gln}]\) ratio means that there's more reactant (\(\alpha\)-KG) than product (Gln). This increase would favor the reaction to move forward, that is, synthesize more glutamine, thus resulting in a decrease in adenylylation level. Therefore, n would decrease.
04

Impact of decline in \(P_{i}\) concentration

A decrease in \(\left[P_{i}\right]\) would slow down the de-adenylylation process as \(P_{i}\) is involved in de-adenylylation. As a result, there would be an increase in the level of adenylylation and therefore the value of n would increase.

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Most popular questions from this chapter

Go to www.pdb.org and examine the pdb file 1 L.M 1 for glutamate synthase. Find its iron-sulfur cluster and FMN prosthetic group. Discover how this enzyme is organized into an N-terminal domain that functions in ammonia removal from glutamine (the glutaminase domain ) and the \(\alpha\) -ketoglutarate-binding site near the \(\mathrm{Fe} / \mathrm{S}\) and flavin prosthetic groups. Consult van den Heuvel, R. H. H., et al., \(2002 .\) Structural studies on the synchronization of catalytic centers in glutamate synthase. Journal of Biological Chemistry 277: \(24579-24583,\) to see how these two sites are connected by a tunnel for passage of ammonia from glutamine to \(\alpha\) -ketoglutarate.

What is the oxidation number of \(\mathrm{N}\) in nitrate, nitrite, \(\mathrm{NO}, \mathrm{N}_{2} \mathrm{O}\) and \(\mathrm{N}_{2}\) ?

Go to www.pdb.org and examine the pdb file 1 L.M 1 for glutamate synthase. Find its iron-sulfur cluster and FMN prosthetic group. Discover how this enzyme is organized into an N-terminal domain that functions in ammonia removal from glutamine (the glutaminase domain ) and the \(\alpha\) -ketoglutarate-binding site near the \(\mathrm{Fe} / \mathrm{S}\) and flavin prosthetic groups. Consult van den Heuvel, R. H. H., et al., \(2002 .\) Structural studies on the synchronization of catalytic centers in glutamate synthase. Journal of Biological Chemistry 277: \(24579-24583,\) to see how these two sites are connected by a tunnel for passage of ammonia from glutamine to \(\alpha\) -ketoglutarate.

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(Integrates with Chapter \(22 .\) ) Write a balanced equation for the synthesis of glucose (by gluconeogenesis) from aspartate.
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