Imino acid
{{distinguish|amino acid|Imidic acid}}
{{short description|Organic compound}}
Image:Delta-1-pyrroline-5-carboxylic acid.svg, an N-substituted imino acid]]
In organic chemistry, an imino acid is any molecule that contains both imine (>C=NH) and carboxyl (-C(=O)-OH) functional groups.{{GoldBookRef|file=I02959|title=Imino acids|accessdate=2012-04-02}}
{{multiple image
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| image1 = Imine-(primary)-skeletal.svg
| caption1 = Imino group attached to carbon
| image2 = Carboxylic-acid.svg
| caption2 = Carboxylic acid
| footer = The two functional groups that together define an imino acid
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Imino acids are structurally related to amino acids, which have amino group instead of imine—a difference of single vs double-bond between nitrogen and carbon. The simplest example is dehydroglycine.
D-Amino acid oxidase is an enzyme that is 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).
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Related terminology
Image:Amminoacido prolina formula.svg]]
Secondary amino acids, amino acids containing a secondary amine group are sometimes named imino acids,{{MeshName|Proline}}{{cite web |url=http://opbs.okstate.edu/5753/Amino%20Acids.html |title= III. Amino Acids | website = Oklahoma State University |access-date=2015-01-03 |url-status=dead |archive-url=https://web.archive.org/web/20080118064634/http://opbs.okstate.edu/5753/Amino%20Acids.html |archive-date=2008-01-18 }} though this usage is obsolescent.{{GoldBookRef|file=I02959|title=Imino acids|accessdate=2012-04-02}} The only proteinogenic amino acid of this type is proline, although the related non-proteinogenic amino acids hydroxyproline{{cite journal | last1 = Myhill | first1 = D. | last2 = Jackson | first2 = D.S. | title = Separation of proline and hydroxyproline using thin-layer chromatography | journal = Analytical Biochemistry | date = 1963 | volume = 6 | issue = 2 | pages = 193–198 | doi = 10.1016/0003-2697(63)90110-6| pmid = 14061301 }}{{cite journal | last1 = Stout | first1 = E.R. | last2 = Fritz | first2 = G.J. | date = 1966 | title = Role of Oxygen Fixation in Hydroxyproline Biosynthesis by Etiolated Seedlings | journal = Plant Physiology | volume = 41 | issue = 2 | pages = 197–202 | doi = 10.1104/pp.41.2.197 | pmid = 16656240| pmc = 1086318 }}{{cite journal | last1 = Blumenkrantz | first1 = N. | last2 = Asboe-Hansen | first2 = G. | title = An assay for hydroxyproline and proline on one sample and a simplified method for hydroxyproline | journal = Analytical Biochemistry | volume = 63 | issue = 2 | date = 1975 | pages = 331–340 | doi = 10.1016/0003-2697(75)90354-1 | pmid = 1122021}} and pipecolic acid{{cite journal |last1= Maruyama |first1= S |last2= Miyoshi |first2= S |last3= Nomura |first3= G |last4= Suzuki |first4= M |last5= Tanaka |first5= H |last6= Maeda |first6= H |title= Specificity for various imino-acid-residues of a proline-specific dipeptidylcarboxypeptidase from a Streptomyces species |journal= Biochim Biophys Acta |year= 1993 |volume= 1162 |issue= 1–2 |pages= 72–76 |doi= 10.1016/0167-4838(93)90129-f |pmid= 8448197 }} have often been included in studies of this class of compounds.
The term imino acid is also the obsolete term for imidic acids, structures containing the -C(=NH)-OH group, and should not be used for them.