Imino acid

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1-Pyrroline-5-carboxylic acid, an N-substituted imino acid

In chemistry, an imino acid is any molecule that contains both imino (>C=NH) and carboxyl (-C(=O)-OH) functional groups.[1]

Imino group attached to carbon
The two functional groups that together define an imino acid

Imino acids are related to amino acids, which contain both amino (-NH2) and carboxyl (-COOH) functional groups, differing in the bonding to the nitrogen.

The D-amino acid oxidase enzymes are able to convert amino acids into imino acids. Also the direct biosynthetic precursor to the amino acid proline is the imino acid (S)-Δ1-pyrroline-5-carboxylate (P5C).

Related terminology[edit]

Amino acids containing a secondary amine group (the only proteinogenic amino acid of this type is proline) are sometimes named imino acids,[2][3] though this usage is obsolescent.[1]

The term imino acid is also the obsolete term for imidic acids, containing the -C(=NH)-OH group, and should not be used for them.[1]


  1. ^ a b c IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Imino acids".
  2. ^ Proline at the US National Library of Medicine Medical Subject Headings (MeSH)
  3. ^

External links[edit]