Amino Acid Metabolism Essential Amino Acids Essential amino

Amino Acid Metabolism

Essential Amino Acids Essential amino acids must be consumed in the diet. Mammalian cells lack enzymes to synthesize their carbon skeletons (a-keto acids). These include: Isoleucine, & valine Lysine Threonine Tryptophan Phenylalanine (Tyr can be made from Phe. ) Methionine (Cys can be made from Met. ) Histidine (Essential for infants. )

Reductive amination catalyzed by glutamate dehydrogenase

Glutamine synthesis is coupled to hydrolysis of ATP

Pyruvate is an amphibolic intermediate in synthesis of alanine

Asparagine synthesis is energetically favorable due to coupling to ATP hydrolysis

Serine biosynthesis

Multistep pathway for glycine biosynthesis

Glycine is also synthesized from serine

Proline biosynthesis

Cysteine is not nutritionally essential, however it is derived from methionine

Tyrosine is formed from phenylalanine

Hydroxyproline is formed after protein synthesis

Selenocysteine is synthesized from serine and selenophosphate

Amino acids that are synthesized de novo in humans. All are related by a small number of steps to glycolysis or TCA cycle intermediates.

Salvage pathways formation of certain nonessential amino acids from other amino acids Amino Acid formed Precursor Amino Acid Arginine Proline Cysteine Methionine Tyrosine Phenylalanine