Chapter 15, Problem 15.73EP

(a)

Interpretation Introduction

Interpretation: To determine whether oxaloacetate is associated with (1) transamination, (2) oxidative deamination, or (3) the urea cycle.

Concept introduction: Transamination reaction is a biochemical reaction that involves the transfer of an amino group. In transamination reaction exchange of an amino group from an $\text{α-amino}$acid with a keto group of $\text{α-keto}$acid. There occurs no net loss or gain of amino acid in transamination reaction.

A biochemical reaction in which an $\text{α-amino}$acid is converted into $\text{α-keto}$acid along with the release of an ammonium ion is known as oxidative deamination reaction.

A urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. The reactants in the formation of carbamoyl phosphate are ammonium ion, water, and carbon dioxide.

Answer to Problem 15.73EP

Oxaloacetate is associated with the transamination reaction.

Explanation of Solution

The structure of oxaloacetate is:

Oxaloacetate contains both a carbonyl group and a carboxyl functional group. Oxaloacetate is a keto acid. It could function as a reactant in the transamination reaction. It reacts with an amino acid to produce aspartate.

(b)

Interpretation Introduction

Interpretation: To determine whether arginine is associated with (1) transamination, (2) oxidative deamination, or (3) the urea cycle.

Concept introduction: Transamination reaction is a biochemical reaction that involves the transfer of an amino group. In transamination reaction exchange of an amino group from an $\text{α-amino}$acid with a keto group of $\text{α-keto}$acid. There occurs no net loss or gain of amino acid in transamination reaction.

A biochemical reaction in which an $\text{α-amino}$acid is converted into $\text{α-keto}$acid along with the release of an ammonium ion is known as oxidative deamination reaction.

A urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. The reactants in the formation of carbamoyl phosphate are ammonium ion, water, and carbon dioxide.

Answer to Problem 15.73EP

Arginine is associated with the urea cycle.

Explanation of Solution

In step 3 of the urea cycle, catalyst argininosuccinate lyase catalyzes the cleavage of argininosuccinate into arginine and fumarate. Arginine formed step 3 reacts with water and undergo hydrolysis in step 4.

Hydrolysis of arginine produce urea and also regenerates the starting fuel ornithine.

(c)

Interpretation Introduction

Interpretation: To determine whether ${\text{H}}_{\text{2}}\text{O}$is associated with (1) transamination, (2) oxidative deamination, or (3) the urea cycle.

Concept introduction: Transamination reaction is a biochemical reaction that involves the transfer of an amino group. In transamination reaction exchange of an amino group from an $\text{α-amino}$acid with a keto group of $\text{α-keto}$acid. There occurs no net loss or gain of amino acid in transamination reaction.

A biochemical reaction in which an $\text{α-amino}$acid is converted into $\text{α-keto}$acid along with the release of an ammonium ion is known as oxidative deamination reaction.  A general oxidative deamination reaction is as follows:

$\text{α-amino acid}+{\text{NAD}}^{+}+{\text{H}}_{\text{2}}\text{O}\to \text{α-keto acid}+{\text{NH}}_4^{+}+\text{NADH}+{\text{H}}^{+}$

A urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. The reactants in the formation of carbamoyl phosphate are ammonium ion, water, and carbon dioxide.

Answer to Problem 15.73EP

Water$\left({\text{H}}_{\text{2}}\text{O}\right)$ is associated with the oxidative deamination reaction and the urea cycle.

Explanation of Solution

Water is one of the reactants in oxidative deamination reaction. For example, glutamate is an $\text{α-amino}$acid it undergoes oxidative deamination reaction to give corresponding keto acid, an ammonium ion, $\text{NADH}$ and ${\text{H}}^{+}$. The reaction is as follows:

Water is also associated with the urea cycle. Ammonium ion produced from oxidative deamination reaction, carbon dioxide, water, and two ATP molecules reacts to form carbamoyl phosphate. Carbamoyl phosphate is fuel for the urea cycle. The chemical reaction for the formation of carbamoyl phosphate is:

(d)

Interpretation Introduction

Interpretation: To determine whether ATP is associated with (1) transamination, (2) oxidative deamination, or (3) the urea cycle.

Concept introduction: Transamination reaction is a biochemical reaction that involves the transfer of an amino group. In transamination reaction exchange of an amino group from an $\text{α-amino}$acid with a keto group of $\text{α-keto}$acid. There occurs no net loss or gain of amino acid in transamination reaction.

A biochemical reaction in which an $\text{α-amino}$acid is converted into $\text{α-keto}$acid along with the release of an ammonium ion is known as oxidative deamination reaction.  A general oxidative deamination reaction is as follows:

$\text{α-amino acid}+{\text{NAD}}^{+}+{\text{H}}_{\text{2}}\text{O}\to \text{α-keto acid}+{\text{NH}}_4^{+}+\text{NADH}+{\text{H}}^{+}$

A urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. The reactants in the formation of carbamoyl phosphate are ammonium ion, water, and carbon dioxide.

Answer to Problem 15.73EP

ATP is associated with the urea cycle.

Explanation of Solution

Adenosine triphosphate (ATP) is a molecule that is defined as the energy currency of life and provides energy to carry out the metabolic processes in the living cells. It is converted either to adenosine monophosphate (AMP) or to adenosine diphosphate (ADP) after the consumption in the metabolic processes.

Step 2 of the urea cycle involves a condensation reaction of citrulline with aspartate to produce argininosuccinate. The reaction is carried out with the expenditure of ATP molecule.