Amino Acid Catabolism

Microbes secrete extracellular proteases to break down proteins into peptides that cross the cell membrane.

Intracellular proteases break down the absorbed peptides into amino acids, which are catabolized via deamination or transamination.

Deamination removes the amino group from the amino acid, forming an organic acid and ammonium ions.

Transamination transfers an amino group to a keto acid, producing a new amino acid and an organic acid.

Ammonium ions released from deamination are excreted as waste to maintain nitrogen balance and prevent toxicity in the cell.

The resulting organic acids are converted to pyruvate, acetyl-CoA, or intermediates of the Krebs cycle.

They can either be oxidized in the Krebs cycle to produce energy or undergo fermentation to generate metabolic intermediates.

In Clostridium species, amino acids are fermented via the Stickland reaction, by coupling oxidation and reduction of amino acids, enabling energy generation efficiently from amino acids when oxygen is unavailable.