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Table A1 Biosynthesis of α-Amino acids. (→ … → denotes “more than one step”)
AA
Synthesized from
Biochemical cycle
Interrelated with
Ref.
Alanine
glutamate and pyruvate
[A1]
Arginine
glutamate →…→ ornithine →…→ citruline →…→ urea cycle
[A2]
Asparagine
Aspartate and ammonia
[A3]
Aspartate and glutamate
Aspartic acid
glutamate and oxaloacetate
[A3]
Cysteine
homocysteine and serine → cystathione
[A4–A7]
glutamine
glutamate an and ammonia
[A8]
glutamic acid
α-ketoglutarate and ammonia
Arginine, glutamine,
proline
[A9]
α-ketoglutarate and an α-amino acid
glutamine
glycine
Serine and tetrahydrofolate
Active methyl cycle
[A9]
histidine
histidinol
metabolism of pentoses and purines
[A9]
Isoleucine
Threonine →…→ 2-oxo-3-methylvalerate
Leucine, valine
[A10]
Leucine
threonine →…→ α-ketoisovalerate → … → 
4-methyl-2-oxopentanoate
Isoleucine, valine
[A10, A11]
Lysine
Aspartate →…→ meso-2,6-diaminoheptanedionate
threonine
[A12]
methionine
Aspartate →…→ homocysteine
Active methyl cycle
[A13]
Phenylalanine
Phenylpyruvate
Prephenate branch of shikamate pathway tyrosine
[A14, A15]
Pretyrosine
Proline
Glutamate → … → δ
1
-pyrroline-5-carboxylate
[A16]
In plants: ornithine
Serine
3-phosphoglycerate → … → 3-phosphoserine
[A17]
threonine
Aspartate →…→ homoserine
Lysine
[A3, A18]
tryptophan
Indole and serine
Anthranilate branch of shikamate pathway
[A14, A19]
tyrosine
Phenylalanine
Prephenate branch of shikamate pathway Phenylalanine
[A14, A20]
p-hydroxyphenylpyruvate
Pretyrosine
valine
Threonine → … → 2-oxoisovalerate
Isoleucine, leucine
[A21]
hydroxyproline Proline (in bacteria)
[A22, A23]
Proline residues in collagen (in plants and animals)