Chapter 15, Problem 15.74EP

(a)

Interpretation Introduction

Interpretation: To determine whether ornithine 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 15.74EP

Ornithine is associated with the urea cycle.

Explanation of Solution

Ornithine is a nonstandard amino acid and accepts the entering carbamoyl phosphate group at the start of each urea cycle. It is encountered in the first step of the urea cycle.

(b)

Interpretation Introduction

Interpretation: To determine whether ${\text{NH}}_{\text{4}}^{\text{+}}$ 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 15.74EP

The ammonium ion $\left({\text{NH}}_{\text{4}}^{\text{+}}\right)$ is associated with the oxidative deamination reaction and the urea cycle.

Explanation of Solution

The ammonium ion is a product of oxidative deamination reaction. A net oxidative deamination reaction is as follows:

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

It is also associated with the urea cycle. It is fuel for the urea cycle however; it is first converted into carbamoyl phosphate and then enters into the cycle. The net urea cycle is as follows:

$\underset{\_}{\underset{\_}{{\text{NH}}_4^{+}}}+{\text{CO}}_{\text{2}}+\text{3ATP}+{\text{2H}}_{\text{2}}\text{O}+\text{aspartate}\to \text{urea}+\text{2ADP}+\text{AMP}+{\text{PP}}_{\text{i}}+\text{fumarate}$

(c)

Interpretation Introduction

Interpretation: To determine whether ${\text{NAD}}^{+}$ 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 15.74EP

${\text{NAD}}^{+}$ is associated with the oxidative deamination reaction.

Explanation of Solution

${\text{NAD}}^{+}$ is a coenzyme. Coenzymes are non-protein organic compounds that are used along with the enzymes and help to carry forward the reaction. Coenzymes cannot perform on their own alone.

Oxidative deamination reaction of glutamate requires dehydrogenase enzyme. It is an oxidoreductase enzyme and works with either ${\text{NADP}}^{+}$ and ${\text{NAD}}^{+}$ coenzyme. It oxidizes glutamate by reducing the coenzyme used.

The oxidative deamination reaction of glutamate amino acid is as follows:

(d)

Interpretation Introduction

Interpretation: To determine whether aspartate 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 15.74EP

Aspartate is associated with the transamination reaction and urea cycle.

Explanation of Solution

Aspartate is a non-essential amino acid. It could function as a product in the transamination reaction.

The reaction is as follows:

Aspartate is also associated with the urea cycle. It is fuel for the urea cycle. It enters directly in step 2 of the cycle and condenses with citrulline to produce argininosuccinate.