Chapter 25, Problem 25.40AP

Interpretation Introduction

(a)

Interpretation:

The sequence of steps for the given reaction involving the adenylation of aspartic acid, is to be determined.

Concept Introduction:

The adenylation of aspartic acid takes place in three steps. In the first step, aspartic acid reacts with ATP. The pyrophosphate is the leaving group in this $S_{N}2$ type of reaction. In the second step, glutamine displaces AMP by a nucleophilic acyl substitution reaction. The intermediate produced in the step 2 undergoes hydrolysis to the form of glutamic acid and asparagine.

Answer to Problem 25.40AP

Step 2:

Step 3:

Explanation of Solution

The adenylation of aspartic acid takes place in three steps.

Step 1: In the first step, aspartic acid reacts with ATP. The pyrophosphate is the leaving group in this $S_{N}2$ type of reaction.

Step 2: In the second step, glutamine displaces AMP by a nucleophilic acyl substitution reaction.

Step 3: The intermediate produced in the step 2 undergoes hydrolysis to the form of glutamic acid and asparagine.

Conclusion

The sequence of steps for the given reaction involving the adenylation of aspartic acid is as shown above.

Interpretation Introduction

(b)

Interpretation:

The utilization of ATP in the equilibrium between glutamine and asparagine, is to be explained.

Concept Introduction:

ATP hydrolysis reactions are highly favorable. The reaction is used to help less favorable reactions which occur in high yield. In the adenylation of aspartic acid, the AMP group is a better leaving group than the hydroxyl group.

Answer to Problem 25.40AP

ATP is highly energetically favorable and produces AMP, which is a better leaving group than $–\mathrm{O}\mathrm{H}$.

Explanation of Solution

To make the less favorable reactions occur in high yield, the high energetic favorability of ATP is utilized. AMP is a better leaving group than $–\mathrm{O}\mathrm{H}$. This favors the amide formation in step 2 shown above.

Conclusion

ATP is highly energetically favorable and produces AMP, which is a better leaving group than $–\mathrm{O}\mathrm{H}$.

Interpretation Introduction

(c)

Interpretation:

The $∆G^0$ for the biosynthesis of asparagine using the given equation, is to be calculated.

Concept Introduction:

The free energy change of two or more reactions can be used to determine the free energy change of a third reaction. The reactions are treated just like algebraic equations.

Answer to Problem 25.40AP

$∆\mathrm{G}{°}^{\mathrm{\text{'}}}=-44.7\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$

Explanation of Solution

$\mathrm{A}\mathrm{T}\mathrm{P}+{\mathrm{H}}_2\mathrm{O}\mathrm{ }\leftrightharpoons \mathrm{A}\mathrm{M}\mathrm{P}+\mathrm{ }\mathrm{p}\mathrm{y}\mathrm{r}\mathrm{o}\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{p}\mathrm{h}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }∆\mathrm{G}{°}^{\mathrm{\text{'}}}=-45.6\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$ (1)

$\mathrm{a}\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{d}\leftrightharpoons \mathrm{ }\mathrm{a}\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{e}+{\mathrm{H}}_2\mathrm{O}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }∆\mathrm{G}{°}^{\mathrm{\text{'}}}=+15.1\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$ (2)

$\mathrm{g}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}+{\mathrm{H}}_2\mathrm{O}\mathrm{ }\leftrightharpoons \mathrm{g}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{d}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }∆\mathrm{G}{°}^{\mathrm{\text{'}}}=-14.2\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$ (3)

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$\mathrm{A}\mathrm{T}\mathrm{P}+\mathrm{a}\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{d}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\leftrightharpoons \mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{A}\mathrm{M}\mathrm{P}+\mathrm{p}\mathrm{y}\mathrm{r}\mathrm{o}\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{p}\mathrm{h}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }$

$+{\mathrm{H}}_2\mathrm{O}+\mathrm{g}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }+\mathrm{a}\mathrm{s}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{e}+\mathrm{g}\mathrm{l}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{d}\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }\mathrm{ }∆\mathrm{G}{°}^{\mathrm{\text{'}}}=-44.7\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$

Conclusion

The $∆G^0$ for the biosynthesis of asparagine is $-44.7\mathrm{ }\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$

Interpretation Introduction

(d)

Interpretation:

The meaning of ATP hydrolysis in biosynthesis of asparagine is to be explained.

Concept Introduction:

ATP hydrolysis is a high energy reaction. It drives other reactions coupled to it, to completion.

Answer to Problem 25.40AP

If ATP is removed from the process, then the reaction is unfavorable. ATP drives the reaction to completion.

Explanation of Solution

If ATP is removed from the process, then the reaction is unfavorable. ATP does not actually undergo hydrolysis, but when coupled to the adenylation of aspartic acid, it becomes favorable and drives the reactions towards completion.

Conclusion

If ATP is removed from the process, then the reaction is unfavorable. ATP drives the reaction to completion.

Interpretation Introduction

(e)

Interpretation:

The reaction that ensures the completion of asparagine biosynthesis, is to be determined.

Concept Introduction:

Pyrophosphatase catalyzes the irreversible conversion of pyrophosphate to phosphate. This reaction ensures the completion of asparagine biosynthesis.

Answer to Problem 25.40AP

The other reaction which drives asparagine synthesis towards completion is the conversion of pyrophosphate to phosphate.

Explanation of Solution

The other reaction which drives asparagine synthesis towards completion is the conversion of pyrophosphate to phosphate, which is irreversible. Pyrophosphate is generated as a by-product during the adenylation of aspartic acid.

Conclusion

The other reaction which drives asparagine synthesis towards completion is the conversion of pyrophosphate to phosphate, which is irreversible.