Amino acid catabolism is a crucial metabolic process that occurs primarily in the liver when the concentration of amino acids exceeds the body's protein synthesis needs. During this process, the amino group of excess amino acids is removed and excreted, as it cannot be stored due to its toxicity. In contrast, the carbon skeleton of the amino acids can be stored and utilized for energy production.
The catabolism of amino acids can be divided into two distinct phases. In Phase 1, the amino group is detached from the amino acid and converted into ammonium ion (\( \text{NH}_4^+ \)), which is then processed through the urea cycle for excretion. It is important to note that not all of the amino group is excreted; some is repurposed to synthesize nitrogen-containing compounds such as hormones, nucleotides, and non-essential amino acids.
Phase 2 focuses on the carbon skeleton of the amino acids, which is transformed into energy-producing intermediates. This phase is closely linked to the Citric Acid Cycle, where the carbon skeleton can be further utilized in gluconeogenesis, the process of generating glucose, and ketogenesis, which involves the formation of ketone bodies. Thus, amino acid catabolism plays a vital role in energy metabolism and the synthesis of essential biomolecules.
