What are the common features of catabolism of all amino acids?

The common features of catabolism of all amino acids involve the removal of the amino group and the processing of the remaining carbon skeleton.

Amino acid catabolism is essential for energy production, gluconeogenesis (glucose synthesis), and ketogenesis (ketone body synthesis). While each amino acid follows a unique catabolic pathway, some general processes are common to all.

Here are the common features:

1. Removal of the Amino Group:

   • The first step in amino acid catabolism is typically the removal of the alpha-amino group (-NH₂). This occurs primarily through transamination.
   • Transamination: Amino groups are transferred from amino acids to alpha-keto acids, often alpha-ketoglutarate, to form glutamate. This reaction is catalyzed by aminotransferases (also called transaminases), which require pyridoxal phosphate (PLP), a derivative of vitamin B6, as a coenzyme.

2. Urea Cycle:

   • The amino group, now often in the form of glutamate, is then converted to ammonia (NH₃). Ammonia is toxic and must be excreted.
   • In mammals, ammonia is converted to urea in the urea cycle, which occurs primarily in the liver. Urea is then transported to the kidneys and excreted in the urine. This pathway effectively detoxifies ammonia.

3. Fate of the Carbon Skeleton:

   • After the amino group is removed, the remaining carbon skeleton (also called the alpha-keto acid) is metabolized to form common metabolic intermediates.
   • These intermediates can enter various pathways, including:
     • Gluconeogenesis: Some carbon skeletons are converted to glucose, making them glucogenic amino acids. Examples include alanine, aspartate, and glutamate.
     • Ketogenesis: Other carbon skeletons are converted to ketone bodies or fatty acids, classifying them as ketogenic amino acids. Examples include leucine and lysine.
     • Both Gluconeogenesis and Ketogenesis: Some amino acids can be converted to both glucose and ketone bodies, such as tyrosine, isoleucine, phenylalanine, and tryptophan.
   • These intermediates ultimately enter the citric acid cycle (Krebs cycle) for complete oxidation to CO₂ and H₂O, generating energy in the form of ATP.

4. Hydrolysis of Peptide linkages

• During protein/peptide catabolism the body hydrolyzes peptide linkages to separate amino acids from each other.

In summary, all amino acid catabolic pathways converge on a few common themes: removal of the amino group, detoxification via the urea cycle, and the conversion of the carbon skeleton into a major metabolic intermediate, thereby contributing to energy production, glucose synthesis, or ketone body synthesis.