Secondary amino acid

Amino acids containing a secondary amine

In organic chemistry, secondary amino acids are amino acids which do not contain the amino group −NH2 but is rather a secondary amine (>NH). Secondary amino acids can be classified to cyclic acids, such as proline, and acyclic N-substituted amino acids.[1][2]

In nature, proline, hydroxyproline, pipecolic acid and sarcosine are well-known secondary amino acids. Proline is the only proteinogenic secondary amino acids. Other secondary amino acids are non-proteinogenic amino acids. In protein, hydroxyproline is incorporated into protein by hydroxylation of proline. Pipecolic acid, a heavier analog of proline, is found in efrapeptin. Sarcosine is a N-methylized glycine so its methyl group is used in many biochemical reactions. Azetidine-2-carboxylic acid, which is a smaller homolog of proline in plants.

## Properties

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Proline and its higher homolog pipecolic acid affect the secondary structure of protein. D-alpha-amino acid - L-alpha-amino acid sequence can induce beta hairpin.[1] It suggested that acyclic secondary amino acids are more flexible than cyclic secondary amino acids in protein by replacement of pipecolic acid by N-methyl-L-alanine in efrapeptin C.[1]

Ninhydrin tests of proline and hydroxyproline give yellow results.

In enzymology, a N-methyl-L-amino-acid oxidase is an oxidase of a subtype of secondary amino acids.

## See also

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* Imino acid
* Imidic acid
* Secondary amine

## References

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1. ^ a b c Konar AD, Vass E, Hollósi M, Majer Z, Grüber G, Frese K, Sewald N (2013). "Conformational Properties of Secondary Amino Acids: Replacement of Pipecolic Acid by N-Methyl-L-alanine in Efrapeptin C". Chemistry & Biodiversity. 10 (5): 942–951. doi:10.1002/cbdv.201300086. PMID 23681735. S2CID 37926505.
2. ^ V V Ryakhovskii; S V Agafonov; Yu M Kosyrev (1991). "Special features of the synthesis of peptides containing secondary amino acids". Russ. Chem. Rev. 60 (8): 924–933. Bibcode:1991RuCRv..60..924R. doi:10.1070/RC1991v060n08ABEH001119. S2CID 250735186.

## External links

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Encoded (proteinogenic) amino acids

General topics|

* Protein
* Peptide
* Genetic code

By properties|

| Aliphatic|

* Branched-chain amino acids (Valine
* Isoleucine
* Leucine)
* Methionine
* Alanine
* Proline
* Glycine

|

Aromatic|

* Histidine
* Tyrosine
* Tryptophan
* Phenylalanine

Polar, uncharged|

* Asparagine
* Glutamine
* Serine
* Threonine

Positive charge (pKa)|

* Lysine (≈10.8)
* Arginine (≈12.5)
* Histidine (≈6.1)
* Pyrrolysine

Negative charge (pKa)|

* Aspartic acid (≈3.9)
* Glutamic acid (≈4.1)
* Selenocysteine (≈5.4)
* Cysteine (≈8.3)
* Tyrosine (≈10.1)

* Amino acids types: Encoded (proteins)
* Essential
* Non-proteinogenic
* Ketogenic
* Glucogenic
* Secondary amino
* Imino acids
* D-amino acids
* Dehydroamino acids

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