Author: Tala Abdallah
Amino acid metabolism is the collective term for the metabolic processes that produce, break down, and use amino acids. The amino groups and ammonia that are provided by the six amino acids are necessary for the synthesis of glutamine and alanine, which muscles release in enormous amounts.
The 6 amino acids metabolized in resting muscle are Leucine, Isoleucine, Valine, Asparagine, Aspartate, and Glutamate. In addition to playing other vital roles in human metabolism, glutamine generated by muscles is an important source of energy and regulates the synthesis of DNA and RNA in the immune system and mucosal cells. Furthermore, protein synthesis and degradation are both required for the organism to maintain balance. Moreover, Acetyl-CoA can only be made by converting leucine and a portion of the isoleucine molecule, and the TCA-cycle intermediates and glutamine are synthesized using the carbon skeleton of the other amino acids.
The breakdown of amino acid carbon skeletons results in the creation of six metabolites: acetyl-CoA, acetoacetyl-CoA, pyruvate, α-ketoglutarate, fumarate, and oxaloacetate and each has a different fate in the energy metabolism. Amino acids are categorized as either ketogenic or glucogenic based on what happens to their breakdown products. Therefore Acetyl-CoA and acetoacetyl-CoA are produced by the ketogenic amino acids leucine and lysine. Many amino acids operate as direct energy-producing substrates and regulate the activity of several enzymes involved in the metabolism of glucose. Both isolated animal and human myocardium exhibit improved contractile performance as a result.
Branched-chain amino acids (BCAAs) are the primary amino acid source for skeletal muscle anabolism and are crucial for maintaining energy balance. Skeletal muscle oxidizes the bulk of the body’s BCAAs, followed by brown adipose tissue, the liver, kidneys, the heart, and other tissues. Skeletal muscle participates disproportionately in BCAA catabolism due to the fact that BCAA transamination, the initial stage of the process, occurs predominantly there.
The amino acid alanine is necessary for the synthesis of proteins and it provides the central nervous system and muscles with energy. The liver uses alanine, which is secreted from skeletal muscle, as a substrate for gluconeogenesis, then the amino group of alanine is changed into urea by the urea cycle, which is then eliminated. The alanine-derived glucose produced in the liver may subsequently be able to re-enter the skeletal muscle and serve as an energy source.
Transamination, a chemical process in which an amino group is added to a keto acid to create new amino acids, is a crucial step in the metabolism of amino acids. The bulk of amino acids undergoes transamination during degradation. Transaminases are specific examples of enzymes that are frequently discovered as markers of potential injury to the liver cells, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST).
Aspartate transferase (AST), an essential enzyme in amino acid metabolism, is found in the liver, heart, pancreas, muscles, and other biological tissues. AST catalyzes a reaction between the amino acids aspartate and glutamate.
An enzyme called aspartate transaminase is released when your muscles or liver are injured and the main sources of AST are liver tissues, myocardium, and striated muscle. Like with all transaminases, aspartate transaminase recognizes two amino acids (Asp and Glu) with different side chains and is able to discriminate between them and bind them.
The quick oxidation of the branched-chain amino acids appears to be connected to the synthesis of alanine in muscle. Alanine is transformed into pyruvate by ALT primarily for cellular energy production moreover the enzyme ALT, which is regarded to be most closely related to the liver, is produced by the kidneys, skeletal muscle, and cardiac muscle. The intermediate metabolism of glucose and protein depends on the enzyme glutamate pyruvate transaminase, often known as alanine aminotransferase (ALT). In order to create pyruvate and glutamate, it catalyzes the reversible transamination of alanine and 2-oxoglutarate.
Leucine, alanine, and proline, three amino acids in particular, suggest they can enhance muscle repair, boost endurance, and grow muscle mass more effectively when paired with other amino acids, carbohydrates, or whey protein. Because glutamine fuels multiple cells throughout the body, it is the best recovery ingredient for all types of exercise. These acids, which are the building blocks of protein, have been demonstrated to help muscle recovery. Beyond protein, glutamine and BCAAs are two of the most important nutrients for athletes to recover and develop muscle, although BCAAs support muscle growth and prevent tiredness glutamine aids in muscle healing and rebuilding after exercise.
For those with muscular dystrophy, defective genes hinder the body from producing the proteins required for proper muscle growth. A serious medical condition called rhabdomyolysis can be fatal or result in permanent disability. Rhabdo arises when muscle tissue is damaged because the electrolytes and proteins are discharged into the bloodstream, for instance, Myoglobin is a protein that is secreted into the bloodstream and then removed from the body by the kidneys which then produces dark-coloured urine.
This article has been prepared from the presentation of our student Tala Abdallah.
Megías M, Molist P, Pombal MA. Atlas of plant and animal histology. http://mmegias.webs.uvigo.es/inicio.html.
Protein Structure, Stability and Folding, Methods in Molecular Biology, 168, Edited by Kenneth P. Murphy
Kubala, Jillian. “Essential Amino Acids: Definition, Benefits and Food Sources.” Healthline, Healthline Media, 6 Feb. 2023, https://www.healthline.com/nutrition/essential-amino-acids.
Vickie E. Baracos, Animal Models of Amino Acid Metabolism: A Focus on the Intestine, The Journal of Nutrition, Volume 134, Issue 6, June 2004, Pages 1656S–1659S
Holeček, M. “The role of skeletal muscle in the pathogenesis of altered concentrations of branched-chain amino acids (valine, leucine, and isoleucine) in liver cirrhosis, diabetes, and other diseases.” Physiological research vol. 70,3 (2021): 293-305.
Choudhary, Ankur. “General Reactions of Amino Acid Metabolism.” Pharmaguideline, https://www.pharmaguideline.com/2022/01/general-reactions-of-amino-acid-metabolism
Wagenmakers, A J. “Protein and amino acid metabolism in human muscle.” Advances in experimental medicine and biology vol. 441 (1998): 307-19.
Mann G, Mora S, Madu G, Adegoke OAJ. Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism. Front Physiol. 2021;12:702826. Published 2021 Jul 20.
Wagenmakers, A J. “Muscle amino acid metabolism at rest and during exercise: role in human physiology and metabolism.” Exercise and sport sciences reviews vol. 26 (1998): 287-314.