Amino Acid Biosynthetic Pathways

In bacteria, amino acids are synthesized from metabolic intermediates such as α-ketoglutarate, pyruvate, oxaloacetate, phosphoenolpyruvate, and erythrose-4-phosphate.

While these intermediates provide the carbon backbone, the nitrogen is incorporated from glutamate or glutamine.

For example, α-ketoglutarate is the precursor for glutamate, which donates amino groups to synthesize glutamine, proline, and arginine.

Transamination of pyruvate and oxaloacetate by transaminases produces simple amino acids such as alanine and aspartate.

The biosynthesis of certain amino acids involves additional steps, including functional group modifications like hydroxylation, methylation, or sulfur incorporation.

For instance, aspartate is first converted to homoserine, which undergoes activation and sulfuration to form homocysteine.

This intermediate is then methylated to produce methionine.

Phosphoenolpyruvate and erythrose-4-phosphate are precursors for the aromatic amino acids phenylalanine, tyrosine, and tryptophan.

While these biosynthetic pathways consume metabolic intermediates, anaplerotic reactions, such as pyruvate carboxylation, replenish them, maintaining metabolic balance.