35. Catabolism of amino acids. General pathways for degradation of the C-skeleton of amino acids. Pathways for degradation of glucogenic and ketogenic amino acids. One-carbon units – types, sources, importance. Vitamin B12, folic acid and S-adenosylmethionine. Therapeutic use of folate analogues. Catabolism of branched-chain amino acids.

BIOCHEM POINT 36: CATABOLISM OF THE CARBON SKELTONS OF AMINO ACIDS …

Fatma Warsame

Catabolism of the Carbon Skeletons of Amino Acids

Amino acids, the building blocks of proteins, undergo metabolism which involves their deamination and the subsequent fate of their carbon skeletons. This process is essential for energy production, synthesis of new compounds, and effective nitrogen balance management in the body.

Deamination:

• Amino acids first have their amino groups removed, primarily through transamination or oxidative deamination.
• This process produces ammonia (which is eventually converted to urea in the liver for excretion) and a keto acid.

Destiny of the Carbon Skeletons:

• The resulting keto acids are further processed in different metabolic pathways, primarily entering the citric acid cycle (Krebs cycle).
• Depending on their structure, these keto acids can be converted into intermediates like pyruvate, acetyl-CoA, or oxaloacetate.

Glycogenic and Ketogenic Amino Acids

Glycogenic Amino Acids:

• These are amino acids whose catabolism yields intermediates such as pyruvate or intermediates of the citric acid cycle (e.g., oxaloacetate, α-ketoglutarate, succinyl-CoA, fumarate).
• Examples include Alanine, Glutamate, Aspartate, and others.
• They can contribute to glucose synthesis through gluconeogenesis.