Amino Acid
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• Proteinogenic amino acid
• Glucogenic amino acid
• Ketogenic amino acid
Proteinogenic amino acid
Proteinogenic amino acids, also known as standard, normal, or primary amino acids, are those 20 amino acids that are found in proteins and that are coded for in the standard genetic code. Proteinogenic literally means protein building. Proteinogenic amino acids are assembled into a polypeptide (the subunit of a protein) through a process known as translation.
Non-proteinogenic amino acids are either not found in proteins (like carnitine, GABA, or L-DOPA), or not coded for in the standard genetic code (like hydroxyproline and selenomethionine). The latter often result from posttranslational modification of proteins.
Some non-proteinogenic amino acids, such as ornithine and homoserine have clear reasons why organisms have not evolved to incorporate them into proteins; both of these amino acids will cyclize against the peptide backbone and fragment the protein with relatively short half-lives.
Some non-proteinogenic amino acids are toxic because they can be mistakenly incorporated into proteins; one example is the arginine analog canavanine.
Glucogenic amino acid
A glucogenic amino acid is an amino acid that can be converted into glucose through gluconeogenesis.[1][2] This is in contrast to the ketogenic amino acids that are converted into ketone bodies.
In humans, the glucogenic amino acids are – glycine, serine, valine, histidine, arginine, cysteine, proline, alanine, glutamate, glutamine, aspartate, asparagine and methionine, while threonine, isoleucine, phenylalanine, tyrosine and tryptophan can be either glucogenic or ketogenic.
References
1. Brosnan J (2003). “Interorgan amino acid transport and its regulation”. J Nutr 133 (6 Suppl 1): 2068S-2072S.
2. Young V, Ajami A (2001). “Glutamine: the emperor or his clothes?”. J Nutr 131 (9 Suppl): 2449S-59S; discussion 2486S-7S.
Ketogenic amino acid
A ketogenic amino acid is an amino acid that can be converted into ketone bodies through ketogenesis. This is in contrast to the glucogenic amino acids that are converted into glucose.
In humans, the ketogenic amino acids are leucine and lysine, while threonine, isoleucine, phenylalanine, tyrosine and tryptophan can be either ketogenic or glucogenic.
