Chapter 17, Problem 27P

Interpretation Introduction

Interpretation:

The balanced reaction for the conversion of pyruvate to alpha-ketoglutarate along with the cofactors and enzymes involved in it should be determined.

Concept introduction:

Metabolism is the chemical processes which takes place within a living organism in order to sustain life. Metabolic reactions can be considered as catabolic and anabolic. Catabolic processes are those in which break down of compounds takes place. Anabolic processes are those in which the synthesis of compounds occurs.

Answer to Problem 27P

The balanced reaction for the conversion of pyruvate to alpha-ketoglutaratealong with the cofactors and enzymes involved in itis given below:

$\begin{array}{l}\text{Pyruvate}{\text{+ CoA + NAD}}^{\text{+}}\underset{\text{dehydrogenas}\text{ecmplex}}{\overset{\text{Pyruvate}}{\to }}\text{Acetyl}{\text{CoA+ CO}}_{\text{2}}\text{ + NADH}\\ \text{Pyruvate}{\text{+ CO}}_{\text{2}}{\text{ + ATP + H}}_{\text{2}}\text{O}\underset{\text{carboxylase}}{\overset{\text{Pyruvate}}{\to }}\text{Oxaloacetate}{\text{+ ADP + P}}_{\text{i}}\text{+}{\text{H}}^{\text{+}}\\ \text{Oxaloacetate}\text{+ Acetyl}{\text{CoA + H}}_{\text{2}}\text{O}\underset{\text{synthase}}{\overset{\text{Citrate}}{\to }}\text{Citrate}\text{+ CoA}\text{+}{\text{H}}^{\text{+}}\\ \text{Citrate}\stackrel{\text{Aconitase}}{\to }\text{Isocitrate}\\ \text{Isocitrate}{\text{+ NAD}}^{\text{+}}\underset{\text{dehydrogenase}}{\overset{\text{Isocitrate}}{\to }}\alpha \text{-ketoglutarate}{\text{+ CO}}_{\text{2}}\text{ + NADH}\\ \text{Net equation:}\text{}\\ \text{2 Pyruvate}\text{+ 2}{\text{NAD}}^{\text{+}}\text{ + ATP}{\text{+ H}}_{\text{2}}\text{O}\underset{\text{carboxylase}}{\overset{\text{Pyruvate}}{\to }}\alpha \text{-ketoglutarate}{\text{+ CO}}_{\text{2}}{\text{ + ADP + P}}_{\text{i}}\text{+}2\text{NADH}+3{\text{H}}^{\text{+}}\end{array}$

Explanation of Solution

The balanced reaction for the conversion of pyruvate to alpha-ketoglutaratealong with the cofactors and enzymes involved in itis given below:

$\begin{array}{l}\text{Pyruvate}{\text{+ CoA + NAD}}^{\text{+}}\underset{\text{dehydrogenas}\text{ecmplex}}{\overset{\text{Pyruvate}}{\to }}\text{Acetyl}{\text{CoA+ CO}}_{\text{2}}\text{ + NADH}\\ \text{Pyruvate}{\text{+ CO}}_{\text{2}}{\text{ + ATP + H}}_{\text{2}}\text{O}\underset{\text{carboxylase}}{\overset{\text{Pyruvate}}{\to }}\text{Oxaloacetate}{\text{+ ADP + P}}_{\text{i}}\text{+}{\text{H}}^{\text{+}}\\ \text{Oxaloacetate}\text{+ Acetyl}{\text{CoA + H}}_{\text{2}}\text{O}\underset{\text{synthase}}{\overset{\text{Citrate}}{\to }}\text{Citrate}\text{+ CoA}\text{+}{\text{H}}^{\text{+}}\\ \text{Citrate}\stackrel{\text{Aconitase}}{\to }\text{Isocitrate}\\ \text{Isocitrate}{\text{+ NAD}}^{\text{+}}\underset{\text{dehydrogenase}}{\overset{\text{Isocitrate}}{\to }}\alpha \text{-ketoglutarate}{\text{+ CO}}_{\text{2}}\text{ + NADH}\\ \text{Net equation:}\text{}\\ \text{2 Pyruvate}\text{+ 2}{\text{NAD}}^{\text{+}}\text{ + ATP}{\text{+ H}}_{\text{2}}\text{O}\underset{\text{carboxylase}}{\overset{\text{Pyruvate}}{\to }}\alpha \text{-ketoglutarate}{\text{+ CO}}_{\text{2}}{\text{ + ADP + P}}_{\text{i}}\text{+}2\text{NADH}+3{\text{H}}^{\text{+}}\end{array}$

The citric acid cycle is a catabolic process. It is a series of chemical reactions in which the stored energy of the body is released by the oxidation of acetyl-Coenzyme A.Flavin adenine dinucleotide is abbreviated as FAD⁺. Nicotinamide adenine dinucleotide is abbreviated as NAD⁺.

Following are the cofactors and enzymes involvedin the conversion of pyruvate to alpha-ketoglutarate are:

1.Pyruvate dehydrogenase enzyme complex: It is required for the linking of glycolysis and TCA. It helps in the conversion of pyruvate into Acetyl CoA. Acetyl CoA then enters into the series of the citric acid cycle.

Pyruvate carboxylase: When the acetyl CoA concentration is high then only the pyruvate carboxylase becomes active. Acetyl CoA might gather in mass if the energy requirements of the cell are not being encountered. It happens due to the deficiency of oxaloacetate. Under these circumstances, the anaplerotic reaction is catalyzed by a pyruvate carboxylase.

Citrate synthase: It is an enzyme that catalyzes the condensation of oxaloacetate with acetyl CoA and forms citric acid.

Aconitase: This enzyme facilitates the isomerizationof the citrate. The isomerization is of stereospecific type in this reaction. It then forms isocitrate in the citric acid cycle. Moreover, it is a non-redox-active process.

Isocitrate dehydrogenase: This enzyme catalyzes the oxidative decarboxylation of isocitrate. It produces a-ketoglutarate and CO2. e. a-Ketoglutarate dehydrogenase is an enzyme which catalyzes the oxidative decarboxylation of isocitrate. It produces a-ketoglutarate and CO₂.

Conclusion

The balanced reaction for the conversion of pyruvate to alpha-ketoglutaratealong with the cofactors and enzymes involved in itis given below:

$\begin{array}{l}\text{Net equation:}\text{}\\ \text{2 Pyruvate}\text{+ 2}{\text{NAD}}^{\text{+}}\text{ + ATP}{\text{+ H}}_{\text{2}}\text{O}\underset{\text{carboxylase}}{\overset{\text{Pyruvate}}{\to }}\alpha \text{-ketoglutarate}{\text{+ CO}}_{\text{2}}{\text{ + ADP + P}}_{\text{i}}\text{+}2\text{NADH}+3{\text{H}}^{\text{+}}\end{array}$