Proline
group of stereoisomers
Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group -NH2 but is rather a secondary amine. The secondary amine nitrogen is in the protonated form (NH2+) under biological conditions, while the carboxyl group is in the deprotonated −COO− form. The "side chain" from the α carbon connects to the nitrogen forming a pyrrolidine loop, classifying it as a aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it from the non-essential amino acid L-glutamate. It is encoded by all the codons starting with CC (CCU, CCC, CCA, and CCG).
Proline is the only proteinogenic amino acid which is a secondary amine, as the nitrogen atom is attached both to the α-carbon and to a chain of three carbons that together form a five-membered ring.
History and etymology
Proline was first isolated in 1900 by Richard Willstätter who obtained the amino acid while studying N-methylproline, and synthesized proline by the reaction of sodium salt of diethyl malonate with 1,3-dibromopropane. The next year, Emil Fischer isolated proline from casein and the decomposition products of γ-phthalimido-propylmalonic ester, and published the synthesis of proline from phthalimide propylmalonic ester.
The name proline comes from pyrrolidine, one of its constituents.
Biosynthesis
Proline is biosynthetically derived from the amino acid L-glutamate.
Begin with the source’s own compact description: “Proline” is group of stereoisomers. The dossier treats that line as a proposition to test through Proline, group and stereoisomers, not as a finished interpretation.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Sep 14, 2026. The linked authority identifier is Q484583. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1900.
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This entry incorporates text from “Proline” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.