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Imino acid[edit]

Why isn't proline an imino acid?

It is... Technichally proteins in the human body are made from 19 typical amino acids and one typical imino acid along with some other infrequently used amino acids.

We should probably correct the article to show that then. According to "Molecular Biology of the Cell, 4th edition" by Alberts et al., page 133, proline is indeed an imino acid.Canadian popcan 04:20, 3 October 2005 (UTC)

According to the IUPAC, Proline IS NOT an Imino Acid or an Amino Acid. It's an azaalkanoic acid. I've modified the article to reflect that. Morwan

Proline is an amino aicd. I.e. it is an amine and it is an acid. It is a secondary amine and it is cyclic, but it is stil an amine - NOT and imine. IUPAC accepts the use of the term "amino acid" and thus it is not necessary to use the (quite uncommon) word "azaalkanoic aicd." (talk) 10:42, 7 January 2008 (UTC)

Energy drinks[edit]

The article currently includes a rather non-encyclopedic blurb about how for some unknown reason, Proline is included as an ingredient in some energy drinks. I am curious about this (as I chug down my Sobe fruit punch)... can anyone add any information to that, to make it more informative? --Norville 14:08, 14 March 2007 (UTC)

Whats really weird about the energy drink citation is that last I checked, you ought not need to look any further than the ingredient label to prove such a thing. Perhaps the person who included the blurb was confused by why proline is in an energy drink in the first place? My feeling, and it is only a feeling, is that a likely explanation is located right above the blurb in question: proline has a flavor! Zaphraud 19:50, 12 July 2007 (UTC)

In bacteria, proline can enter the Krebb's cycle and provide a secondary energy source by first being converted to glutamate. In animals, the availability of proline to the Krebb's cycle is restricted by slow transport across the mitochondrial membrane. So, although Sobe thinks they are providing an energy source, it would only be so if you were a bacteria. Kevin.stafford 16:53, 17 April 2007 (UTC)kevin.stafford April 2007


I am a graduate student of biochemistry, and even I had trouble understanding some of the statements regarding proline - particularly the last section before the energy drink blurb. I imagine that an average Wikipedia reader would not be able to understand much beyond the intro and the trivia at the end. While I am glad to see a wealth of information here, it should be at least somewhat accessible to a reader who has only cursory knowledge of biochemistry and proteins. I reworded a few sentences, added links, and added an explanation for the "X" that comes out of nowhere in the cis-trans section, but someone with more knowledge/skills could improve it further. I think this is one of the better amino acid articles, and I'd like to see it become even better. GngstrMNKY (talk) 21:52, 2 February 2008 (UTC)

Please specify exactly what is not clear, so I can help.

Why external link have been removed?[edit]

Dear Dirk Beetstra, I would be very grateful if you could explain why you removed external link ? Is the following page more relevant than my link?

Thanks in advance! —Preceding unsigned comment added by (talk) 14:54, 11 March 2008 (UTC)


The statement "such as sarcosine; symbol is X, as is true for all non-standard amino acids" is incorrect. X is used in peptide/protein chemistry in two instances (1) Unknown amino acid: as in could not be determined from sequencing and (2) Variable amino acid: as in X can be any amino acid, equivalent to a wildcard character. The acceptable symbol for Sarcosine is Sar although some also consider MeGly acceptable. The X convention is properly applied later in the section. If there are no objections I'll update the section. Atomjockey (talk) 18:58, 19 June 2008 (UTC)

References and Conformations[edit]

There are several places were more detailed referencing is needed (IMO). Unfortunately, our access to ACS journals is rather limited. If anyone out there can get these articles, I think they could make a nice addition.

Conformational Analysis of L-Prolines in Water Aliev, A. E.; Courtier-Murias, D. J. Phys. Chem. B.; 2007; 111(50); 14034-14042. DOI: jp076729c

Conformational Studies of Polyprolines Zhong, H.; Carlson, H. A. J. Chem. Theory and Comput.; 2006; 2(2); 342-353. DOI: ct050182t

Also, there is presently no discussion of Φ, ψ angles nor of the importance of Pro in β-turns Atomjockey (talk) 18:48, 20 June 2008 (UTC)

Keep journal references to a minimum, please!~[edit]

Although journal references are kinda impressive, they threaten to overwhelm Wikipedia. Also we dont want Wikipedia to become a forum for researchers to broadcast their (specialized) achievements, because that trend would be difficult to stop. Rather than highly specialized references (JPhysChem published 47148 pages last year), editors should search for the key material (e.g., on Φ, ψ angles, β-turns for proline) in textbooks and conventional reference sources where the perspective is broader and the sources are more accessible. IMHO. Journal refs might be reserved for seminal discoveries (e.g. of the amino acid).--Smokefoot (talk) 22:13, 20 June 2008 (UTC)

Proline's role in plants[edit]

Dear Authors,

I think it would be nice to mention proline's role in plants, and stress tolerance (salt stress and draught especially)(it has quite a significant role there, so it shouldn't really be left just like this, without a word.).

Have a look at the following articles for example:

=)Please, please, do something! THANKS!!!Myrmeleon formicarius (talk) 14:58, 21 January 2009 (UTC)

efeeeeeeeeew abdul —Preceding unsigned comment added by (talk) 15:41, 3 February 2010 (UTC)


The reference for proline's solubility in ethanol is a search for "methionine solubility in ethanol". Methionine is not the same compound as proline. Johnjohnston (talk) 04:44, 16 February 2014 (UTC)

Fixed Cleaned up the cite. TuxLibNit (talk) 23:01, 28 February 2014 (UTC)

Molecular Formula[edit]

What's the molecular formula?
Eg: Phenylalanine has a chemical formula of C9H11NO2 but a molecular forumla of C6H5CH2CHCOOH
~ender 2014-10-06 5:52:AM MST — Preceding unsigned comment added by (talkcontribs) 12:55, 6 October 2014 (UTC)

for the condensed formula see here Jytdog (talk) 13:15, 6 October 2014 (UTC)
OP posted this on several amino acid pages; please see discussion here: Talk:Tryptophan#Molecular_Formula Jytdog (talk) 14:17, 6 October 2014 (UTC)


I was told that L-Proline can be synthesized using Knowles Asymmetric Hydrogenation. I was wondering if someone with more experience on this could please elaborate? — Preceding unsigned comment added by (talk) 17:05, 11 November 2014 (UTC)

Wikipedia is not a scientific manual - that is very technical information that doesn't belong in an encyclopedia article. You can read about that here, though: Jytdog (talk) 17:38, 11 November 2014 (UTC)

cis-trans isomerization[edit]

The article has the text "Most peptide bonds overwhelmingly adopt the trans isomer (typically 99.9% under unstrained conditions), chiefly because the amide hydrogen (trans isomer) offers less steric repulsion to the preceding Cα atom than does the following Cα atom (cis isomer)." If a citation can be given for this, then that is great. However, I think the problem is worse and that this statement is wrong. At the very least, here is one reference suggesting that it is the sidechain-sidechain interaction that favors the trans isomer of the peptide bond: — Preceding unsigned comment added by (talk) 02:27, 6 September 2015 (UTC)

23 Proteinogenic amino acids?[edit]

Proteinogenic amino acid says there are 22. I'm not clear enough to tell whether there's some subtlety, but it seems to me that, unless someone can come up with what number 23 is, we should go with 22.--Wcoole (talk) 00:22, 27 October 2015 (UTC)

Standardizing amino acids[edit]

There is a lot of inconsistency regarding what information is presented by the introductory paragraph. I think it would be great to standardize this information. As in have all 20 main amino acids follow a common template. Furthermore, the addition of the ionized (native biological state) of the amino acid alongside the historically represented line-angle model would provide a more factual representation of their states

Linnikh (talk) 00:05, 18 November 2015 (UTC)

Assessment comment[edit]

The comment(s) below were originally left at Talk:Proline/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Please I recently learnt that L-Proline is converted to D-Proline which is a known toxin that attacks human internal organs and nervous system. (Lancet Dec. 9th 1989)Please are there other sources for further reading on this topic? Milko Johnson217.43.176.54 (talk) 16:53, 6 January 2008 (UTC)

Last edited at 16:53, 6 January 2008 (UTC). Substituted at 03:26, 30 April 2016 (UTC)


The following is unsourced - moving here per WP:PRESERVE

Proline is a phosphorylation marker and is commonly found right before the amino acid serine and threonine to mark them as phosphorylation spots. As a result, proline preceding these amino acids in an amino acid chain is highly evolutionarily conserved.

-- Jytdog (talk) 18:39, 16 August 2016 (UTC)