Difference Between Glucogenic and Ketogenic Amino Acids

Main Difference – Glucogenic vs Ketogenic Amino Acids

Amino acids are the building blocks of proteins and polypeptides. These are organic compounds composed of C, H, O and N atoms. Amino acids can be categorized into two main groups as essential amino acids and non-essential amino acids. Essential amino acids are amino acids that cannot be synthesized in our body whereas non-essential amino acids are amino acids that can be synthesized by the human body. In addition, amino acids can be classified into three groups based on the catabolism. They are Glucogenic amino acids, Ketogenic amino acids and mixed amino acids (both Glucogenic and Ketogenic). The main difference between glucogenic amino acids and ketogenic amino acids is that glucogenic amino acids can be converted into pyruvate or other glucose precursors whereas ketogenic amino acids can be converted into acetyl CoA and acetoacetylCoA.

Key Areas Covered

1. What are Glucogenic Amino Acids
      – Definition, Examples
2. What are Ketogenic Amino Acids
      – Definition, Examples
3. What is the Difference Between Glucogenic and Ketogenic Amino Acids
      – Comparison of Key Differences

Key Terms: Amino Acids, Essential Amino Acids, Glucogenic, Gluconeogenesis, Ketogenesis, Ketogenic, Polypeptides, Proteins

What are Glucogenic Amino Acids

Glucogenic amino acids are amino acids that can be converted into glucose via gluconeogenesis. In amino acid catabolism, Glucogenic amino acids form pyruvate or other glucose precursors as an intermediate. Here, other glucose precursors include alpha-ketoglutarate, succinyl Co-A, Fumarate, and oxaloacetate.

Almost all essential and non-essential amino acids (except lysine and leucine- these are also essential amino acids but are Ketogenic amino acids) are Glucogenic amino acids. Therefore, Glucogenic amino acids include alanine, arginine, asparagine, aspartic, cysteine, glutamic, glutamine, glycine, histidine, methionine, proline, serine and valine.

Figure 1: Amino Acid Catabolism

The above image shows amino acid catabolism. The amino acids in red color are Glucogenic amino acids. These amino acids are shown with the intermediate precursor they can form. For example, alanine can convert into pyruvate, and this pyruvate is then converted into glucose via gluconeogenesis in the liver.

What are Ketogenic Amino Acids

Ketogenic amino acids are amino acids that form acetyl CoA or acetoacetylCoA. These are precursors for ketone bodies. These amino acids cannot produce glucose. This is because the carbon atoms in the ketone body are degraded into Carbon dioxide in the citric acid cycle.

The most common Ketogenic amino acids are lysine and leucine. These are essential amino acids. Some amino acids are considered as both Glucogenic and Ketogenic since they can give rise to both glucose precursors and fatty acid precursors. This group includes isoleucine, phenylalanine, threonine, tryptophan, and tyrosine.

Figure 2: Ketogenesis

Although Ketogenic amino acids fail to produce glucose, they can be used for ketogenesis or lipid synthesis. Ketogenesis is the biochemical process of forming ketone bodies from the breakdown of Ketogenic amino acids or fatty acids. Ketone bodies are in three types as Acetoacetate, Acetone, and β-hydroxybutyrate.

Difference Between Glucogenic and Ketogenic Amino Acids

Definition

Glucogenic Amino Acids: Glucogenic amino acids are amino acids that can be converted into glucose via gluconeogenesis.

Ketogenic Amino Acids: Ketogenic amino acids are amino acids that form acetyl CoA or acetoacetylCoA.

Precursors

Glucogenic Amino Acids: Glucogenic amino acids form glucose precursors.

Ketogenic Amino Acids: Ketogenic amino acids form precursors for ketone bodies.

Importance

Glucogenic Amino Acids: Glucogenic amino acids are important in gluconeogenesis.

Ketogenic Amino Acids: Ketogenic amino acids are important in Ketogenesis.

Examples

Glucogenic Amino Acids: Most essential and non-essential amino acids are Glucogenic amino acids.

Ketogenic Amino Acids: Lysine and leucine are exclusively Ketogenic amino acids.

Conclusion

Amino acids are building units of proteins. Some amino acids are essential (cannot be synthesized in the body) where other are non-essential because they can be synthesized inside the body. Amino acids can be either glucogenic or ketogenic depending on their catabolism. The main difference between glucogenic amino acids and ketogenic amino acids is that glucogenic amino acids can be converted into pyruvate or other glucose precursors whereas ketogenic amino acids can be converted into acetyl CoA and acetoacetylCoA.

References:

1. “Glucogenic and ketogenic amino acids (Practice).” Khan Academy,  Available here.
2. “Ketogenic amino acid.” Wikipedia, Wikimedia Foundation, 13 Oct. 2017, Available here.
3. “Ketogenesis.” Wikipedia, Wikimedia Foundation, 11 Nov. 2017, Available here.

Image Courtesy:

1. “Amino acid catabolism revised” By Mikael Häggström -(CC0) via Commons Wikimedia
2. “Ketogenesis” By Sav vas – Own work (CC0) via Commons Wikimedia