Talk:Cysteine

Permanent wave applications
 In the field of personal care Cysteine is used for permanent wave applications predominantly in Asia. What does "permanent wave applications" mean? If this means to shape hair like waves, I think people would use this technique worldwide. Could somebody clarify this? --NormalAsylum (talk) 19:20, 19 July 2005 (UTC)

See permanent wave and ammonium thioglycolate for an explanation. Walkerma 06:34, 10 January 2006 (UTC)

The structural formula vs the ball and stick and 3D
They are clearly not the same molecule. According to the systematic name, (R)-2-Amino-3-sulfanylpropionic acid the ammino group should be attached to the second carbon aton in the chain, as in the structural formula, not the first. And sulphur should not be binding two hydrogen atoms, should it? The poor second C-atom, on the other hand is a hydrogen atom short! (no sig)

No, different order, but equally screwy. Compared to the Skeletal diagram, the sulfur branch is fine (yellow). The violet atom has 3 hydrogens, should be NH2; the key says 'blue' is nitrogen, doesn't say what violet is. Then the COOH, should be H-O-C=O not O=C=O OsamaBinLogin (talk) 00:40, 8 March 2021 (UTC)

no I got it; explanation in talk for Tyrosine. "at physiological pH", the H on the end of the carboxyl moves to the N to make NH4 (see skel for tyrosine). Yes this is confusing, and is wasting our time. OsamaBinLogin (talk) 00:49, 8 March 2021 (UTC)


 * The skeletal formula is drawn neutral but the reality is cysteine exists as a zwitterion in most circumstances. The 3D models are based on the crystal structure of solid cysteine determined by X-ray diffraction, reported in Acta Cryst. E (2005) 61 o2739-o2742 (CSD entry LCYSTN22). It's really the skeletal formula that is misleading. The article on glycine has more details and diagrams illustrating these points. I've fixed the colour labels. --Ben (talk) 00:51, 8 March 2021 (UTC)

Hydrophobic vs. hydrophilic
My Biology textbook by Campbell and Reece says that Cysteine is a hydrophilic amino acid.


 * What about this?
 * Ben 12:00, 1 June 2006 (UTC)

I agree: Hydrophilic for sure. See "Lehninger Principles of Biochemistry" Nelson and Cox, p.80, pub. W. H. Freeman and Co. It states clearly that cysteine is hydrophilic.

Also, "Handbook of Chemistry and Physics", 63rd Ed., p.C-259, pub. CRC Press, says cysteine is soluble in water.

The hyperlinked reference above is absolutely mistaken. In fact, it doesn't even make sense. It shows clearly that the molecule is short, and states and shows that it is quite polar. These facts being true, it can't possibly be hydrophobic, as it states. I can supply numerous other references, but that would be obtuse.


 * Cystine, however is hydrophobic. The solubility characteristics of both molecules are predictable by looking at their structures. Cystine is almost perfectly non-polar, while cysteine is quite polar. I do not believe there is any controversy, and move to correct the article. Psyber93157 04:50, 10 November 2007 (UTC)


 * All amino acids are soluble in water, because they are loaded with polar covalent bonds in their backbones. But that's not relevant to their behavior in proteins, where some of those polar covalent bonds have been lost in polymerization, and it's the R groups that determine classification as hydrophilic vs. hydrophobic. See 2012 section below for more on this. Jbening (talk) 22:43, 16 September 2012 (UTC)

--

It is polar, and polar means hydrophilic, not hydrophobic. The currently cited source says "Polar and charged amino acids are hydrophilic" so can someone just edit it? — Preceding unsigned comment added by 85.24.222.57 (talk) 14:31, 3 February 2012 (UTC)


 * See 2012 section below. Jbening (talk) 22:41, 16 September 2012 (UTC)

Hangover Reducing Properties
I think it shoud be mentioned somewhere that Cysteine helps treat hangovers. I'll try to find some hard evidence but I've seen it mentioned on many websites and it has worked for me.

Pronunciation
Could somebody please add the pronunciation for cysteine?

Usually pronounced, 'sis-tuh-een. Psyber93157 05:05, 10 November 2007 (UTC)

New infobox
I'm liking the new infobox :). However, when I clicked on H in the chemical formula, it sent me to helium! Who can fix it?  Ben 17:15, 23 March 2006 (UTC).


 * It's OK, I've fixed it. Ben 17:19, 23 March 2006 (UTC).


 * Good job, Ben. -- Boris 23:28, 23 March 2006 (UTC)

Hydrophilic or not
Alright, i wasn wrong about SH being more polar than OH, my bad. Still SH is a polar group. The H-bonds it forms isn't very strong but that doesn't make it hydrophobic, does it. -- Boris 00:27, 1 June 2006 (UTC)


 * I think it does. Thiols have different physical properties from alcohols for exactly that reason: practically non-existant hydrogen bonds. Maybe I'm wrong, though, I'll do some research. If the situation turns out to be complicated, we should leave the question of hydrophilicity out of the first sentence and discuss it in detail later in the article. —Keenan Pepper 05:15, 1 June 2006 (UTC)


 * Check out this beauty. It's a table of hydrophobicities of the amino acids.  It shows that cysteine is more hydrophobic than alanine and glycine, but less so than proline and methionine.


 * Hydrogen bonds are defined as bonds of the form X-H---Y, where X and Y are chosen from F, O or N. The S-H bond is not polarized enough to do hydrogen bonding, the electronegativity of sulfur being 2.58 and that of hydrogen being 2.20.  Thus the electronegativity difference in the S-H bond is only 0.38, which is not quite enough to be considered a polar covalent bond (0-0.4 = non-polar, 0.4-1.7 = polar, 1.7+ = ionic).


 * Ben 12:22, 1 June 2006 (UTC).


 * That's a good finding, Ben. This table could go on the amino acid page with the appopriate citation. Strangely, the difference between Cys and Met (one more methyl-group than Cys) is ~ 0.6 only, while between Val and Ile (same difference) is ~ 1.2.-- Boris 00:24, 2 June 2006 (UTC)


 * The current version of the text is fine by me. Cys-side chain apparently isn't hydrophilic, but i can't call it hydrophobic either. Cys itself, with it's amino and carboxy groups, is hydrophilic and there is no doubt about it. -- Boris 00:24, 2 June 2006 (UTC)


 * Boris, the current text states that it is hydrophobic. I agree with your conclusion, that it is undoubtedly hydrophilic, but the article does need to be corrected to say that. Psyber93157 05:10, 10 November 2007 (UTC)


 * See 2012 section below. Jbening (talk) 22:40, 16 September 2012 (UTC)

Sheep
If sheep cannot make cysteine out of methonine, which enzyme do they miss? Cysteine is not only in grass, so when sheep eat some oher foodstuff, they are not automatically low in cysteine. When they stop eating anything at all, they die with and without wool.

I've never heard before, that sheep are missing an enzyme, what all other mammals and ruminants have, what makes methionine to cysteine.

Cysteine and methionine are both S containing amino acids. There are such a few naturally occuring situations, that a sheep is getting enough methionine but not enough cysteine. Therefore, the sum of them both is essential and you shuld not forget to feed enough S-containing amino-acids and please do not feed just cysteine.

The whole sheep stuff in the article is not necessary, at most semi-true and should be deleted. —Preceding unsigned comment added by Jrockley (talk • contribs)
 * No, the story seems to be true, a short google survey (sheep cysteine) gives some sites which seem to support this story. Wool is dependent on cysteine, and they need a lot of it for wool.  And they are dependent on it from their diet.  --Dirk Beetstra T  C 21:16, 20 July 2006 (UTC)

I don't understand this sentence. I move to cut it. .A little concentration of cysteine is used to break the disulfide bonds during the solublisation of recombinant protein preparation.
 * 1) First of all this is not a common biochemical technique.  There are far better reducing agents like dithiothreitol,  &beta;-mercaptoethanol, and  TCEP.
 * 2) Second what does protein purification techniques have to do with sheep?

[edit]

Merge
It seems to me Cystine is a dimer of Cysteine, but the articles seem confused on this. A lot of the content is replicated, so I suggest a merge - Jack (talk) 20:34, 20 July 2006 (UTC)


 * Support merge. Everything from Cystine should go into this article or Disulfide bond. —Keenan Pepper 20:37, 20 July 2006 (UTC)


 * Ambivalent about merge. They are two different chemical compounds, different sources, though closely related.  Overlap should maybe be removed, but I do not have any objection against short compound pages.  If there is nothing more to tell, there is nothing more to tell, so?  --Dirk Beetstra T  C 21:05, 20 July 2006 (UTC)
 * Against merge. I don't think merging is worth the effort in this case. There is obviously overlap between the two articles, but they are distinct chemical compounds, and I think they each warrant a separate article.  The replicated content can be reduced and some thoughtful editing can deal with the confusion. As the articles mature, they will continue to diverge in content.  --Ed (Edgar181) 03:16, 21 July 2006 (UTC)
 * Against merge. Cystine and cysteine act very differently in the body and are quite different in their structure. I believe they warrant separate articles.  Since both are the building blocks for GSH (glutathione) but only one is fractionated interecellularly (cystine) and one provides twice the quantity of the base molecule (cystine) while being associated with a completely different side effect profile (cysteine is more toxic), they are physiologically and chemically quite different compounds.  The free amino acid cysteine (as supplied by NAC) does not represent an ideal delivery system to the cell. It is potentially toxic and is spontaneously catabolized in the gastrointestinal tract and blood plasma. Conversely, cysteine absorbed during digestion as cystine (two cysteine molecules linked by a disulfide bond) in the gastrointestinal tract is more stable than the free amino acid cysteine.  Cystine travels safely through the GI tract and blood plasma and is promptly reduced to the two cysteine molecules upon cell entry. Cysteine dosing (as NAC) is limited to to CNS side effects such as headache and dizziness.  There are no such SEs associated with cystine to my knowledge. Cystine is the preferred form of cysteine for the synthesis of glutathione in macrophages and astrocytes. Lymphocytes and neurons prefer cysteine for glutathione production optimizing glutathione levels in macrophages and astrocytes with cystine allows these cells to provide cysteine to lymphocytes and neurons directly upon demand. Additionally, Cystine and Cysteine usually occur as separate entries in lists of common amino acids. In summary: They are different compounds both physiologically and chemically.  I believe they should be kept separate. Apparent Logic 12:39, 28 July 2006 (UTC)
 * Against merge. These are two different, albeit related chemical species, with different physical and chemical properties. A  redox reaction is required to make one from the other. Psyber93157 04:31, 10 November 2007 (UTC)

Why do they put it in cigarettes?
"Its use or purpose, however, is unknown, like most cigarette additives."

I don't think that's true; I think they use it for a well-known reason. Anyone know what it is? —Keenan Pepper 18:52, 27 July 2006 (UTC)
 * Two thoughts: Cystine can act as an expectorant, breaking the disulfide bonds in the mucus and making it more liquid, facilitating clearing it from the lungs. Mucus production increases in smokers. Secondly, cystine is one of the rate limiting substrates (building blocks) for glutathione (GSH), one of the most potent antioxidants in the human body.  Smoking reduces GSH. Increasing cystine would increase GSH in most folks, and this would be a benefit especially to smokers. Apparent Logic 13:49, 28 July 2006 (UTC)


 * The list is of 'approved' additives, that means that they can be used, not that they are. This needs fixing as well as the removal of the speculation as to why it might be used.Muleattack (talk) 02:13, 30 June 2011 (UTC)

Ok. I perhaps we cannot (as yet) know the cigarette companies _intentions_ but we can say that as it is on the list it may be being added. and if it is added it is likely to have an effect in the lungs. this effect is very well known because cysteine is inhaled, the standard treatment for cystic fibrosis for 30years, and this liquifies mucus by breaking disulfide bonds. exactly correct. also this is the same reasoning for anything else in cigarettes. ie we cannot really know why anything, including say menthol or cloves are added. can we even truely say we know "the intention" behind nicotine? ... why should any (relative) uncertainty about motives preclude disemination of the necessary concequences. A does B, lets not delete that because we dont really know that Z specifically includes A for B. Shit for all I know they also include 5-halo-uracil as a radio-sensitiser.

Human Hair Source
Reference to human hair cheapest source and vague references to manufacturers in China have been repeated endlessly by internet angst sites. Until a reliable source surfaces, I have removed all reference to "human hair" from this article. All such stories appear to reference back to a single article in the Japanese publication ```Mainichi``` and an article about human hair in soy sauce. Norm Reitzel (talk) 20:40, 10 September 2009 (UTC)


 * If a future reference is needed for this, then Jamie Olivers Food Revolution Series 2 Episode 3 details the use of human hair in the production of l-cysteine. http://www.youtube.com/watch?v=SpWvoj-IGJk — Preceding unsigned comment added by Muleattack (talk • contribs) 01:54, 30 June 2011 (UTC)


 * This reference is just a dead link. There's no reason to think the use of human hair is more than an internet rumour. Seriously, you would literally need tons of hair, which would be much cheaper from non-human sources. I've removed these references (again). Dhall27 (talk) 15:53, 5 February 2016 (UTC)

Insulin inactivation
Reads like pseudoscience to me, particularly since there are millimolar concentrations of GSH in blood already. Unless a reliable source actually describes this (nothing in PubMed and Anti-aging News is certainly NOT reliable) this does not belong in the article. Tim Vickers (talk) 22:57, 20 October 2009 (UTC)

Metabolism of Glutathione V. an effect of insulin by francis binkley, gerald M christensen and feng chi wu pub" march 30,1951 dept of pathology and biological chemistry, university of utah

http://www.jbc.org/content/192/1/29.full.pdf

Also AlphaLipoicAcid, a thioreductant and so cysteine would be a feedstock, is well known to improve blood sugar control.

Tim you didnt look very hard; i googled "glutathione and insulin" and was inundated. oh glutathione is a tripeptide involving cysteine. — Preceding unsigned comment added by 220.101.100.14 (talk) 22:18, 23 May 2012 (UTC)

polar vs hydrophobic again
Discussion above seems to agree that it is hydrophyllic to some extent, yet the text remains hydrophobic. Elsewhere wikipedia lists it as polar --68.35.2.8 (talk) 13:50, 15 April 2011 (UTC)
 * See 2012 section below. Jbening (talk) 22:39, 16 September 2012 (UTC)

Isomerism
Could someone please explain to me why L-Cysteine is allegedly R? Under the rules I was taught, and as listed on Cahn–Ingold–Prelog_priority_rules Wikipedia, mass only comes into it when they are the same element just different isotopes (such as Deuterium and Hydrogen). Also, double bonds are treated as 2 bonds to the same atom. Therefore, C=OO counts as having 3 oxygen atoms and thus has a priority of 3*8 or 24. The side chain has a sulphur and 2 hydrogens, giving a priority of 2*1+16 or 18. This is still well below the 24 of the carboxyl group, and thus the carboxyl group has a higher priority, and thus the L form should still be the S form, not the R form. The one which the L form is the R form is selenocysteine, which has selenium in the place of sulfur, giving that chain a priority of 32+2 or 34, making it higher than the carboxyl group. Unless I get a satisfactory explanation, I will change it in a week (and on the amino acid page). — Preceding unsigned comment added by 149.171.197.22 (talk) 01:49, 16 August 2011 (UTC)
 * Answered you on Talk:Amino acid. Executive summary: you're not determining the CIP precedences correctly. DMacks (talk) 01:59, 16 August 2011 (UTC)

One little question
I'm confused with a phrase "dietary sources". Does this refer to "dietary" like something connected to diet when we want to loose our weight? - Cause it doesn't have any sense to me. Other translation I can use is only one I can get from mine translation tool and it's meaning is "soources in order (sequence sources)". I hope I'll get some answer. Thanks. Oblak24 (talk) 17:05, 19 October 2011 (UTC)

Hi Oblak24. I'm a biochemist. I can answer your question. I just don't understand it in it's current form. Can you rephrase it and let me know about it on my talk page? A dietary source just means a source in your diet containing Cysteine. — Preceding unsigned comment added by Carstensen (talk • contribs) 23:08, 19 October 2011 (UTC)

Hi Carstensen, You may be able clear my mind too..

I am reading into the use of L-Cysteine in baking and I see also on the article page that there is the use of a 'mutant?' of E.Coli. Now aside from the vegetarian question, E.Coli (from my past involvement in a food production environment) comes from human excrement does it not? This is very uncomfortable for me at the moment, could you please tell me what relationship there is if any all the way from excrement(!) to Baking!

Thank you very much in advance, Abu-bakrUK (talk) 00:39, 13 January 2012 (UTC)


 * First off, E.coli is a coliform bacterium that occurs naturally in very many places, including as colon bacteria in many species including humans. Because it is so widespread and very easy to grow in cultures, the organism is often used for producing proteins, antibodies, amino acids, and all sorts of organic products.  GMO bacteria have been in use for at least half a century, with all variety of genes spliced into the organism to produce some product that humans want or need.  None of these bacteria used to produce products ever came from human (or other) excrement, they are cultured in laboratories under completely sterile conditions.


 * Producing L-Cysteine from bacteria (yes, E.coli are used) involves filtering the bacterium from a culture, killing the organism (usually with heat), breaking down the cell walls, and then separating out the product desired from all the cell detritus. Note that this is no different than obtaining cinnamon oil by ripping off living bark from a tree, grinding it up, and extracting the desired product. No fecal material is involved in the cycle at any stage whatsoever. Norm Reitzel (talk) 17:10, 13 January 2012 (UTC)

Cysteine
this section is confusing, how does it relate to Cysteine? Hogdotmac (talk) 23:21, 4 April 2012 (UTC)

shameful advertising attempt
wow whoever added the link to the subject title "precursor to glutathione" should be ashamed of themselves. Advertising bogus pseudo-scientific product crap on wikipedia completely defeats the purpose. Get out and don't come back. — Preceding unsigned comment added by 130.195.203.47 (talk) 05:41, 4 July 2012 (UTC)
 * I have now removed it. I can't believe it sat there in the article for so long. In the future, you or anyone else can remove that kind of spam yourself.  -- Ed (Edgar181) 14:24, 12 December 2012 (UTC)

Hydrophilic vs. hydrophobic 2012
I've just reorganized and reworded the material describing the chemical behavior of cysteine in proteins, adding more refs. While cysteine has traditionally been classed as hydrophilic, and while some of the more traditional sources do still class it as such, the actual evidence (some cited in the article) supports hydrophobicity. Add to this that the SH bond in cysteine isn't an especially polar bond by nature, and its accepted hydropathy value (given in the amino acids WP article) places it above many traditionally hydrophobic amino acids, and well above the hydrophilic amino acids. I'm certainly open to further discussion of this, but preferably if such discussion includes contrary data, rather than just citations to sources that may merely have taken the path of least resistance in keeping cysteine classed as it had been a generation ago.Jbening (talk) 20:50, 16 September 2012 (UTC)
 * Excellent work, thanx.--Africangenesis (talk) 23:27, 3 October 2012 (UTC)

Cysteine and L-Cysteine
The article starts out talking about "cysteine", then, without any explanation, begins talking about "L-cysteine", as if the terms were interchangeable. For people who know about chemistry, the significance of the "L-" prefix may be quite obvious, but I, for one, would appreciate some explanation in the lede, or at the first mention of "L-cysteine". Reading down to the "Applications" section, I learn that there is something called an "L-enantiomer", and following the link leads me to understand that cysteine molecules may appear in left-handed or right-handed form, so to speak. This information leads me to speculate that L-cysteine may be the left-handed version, or L-enantiomer, of cysteine; but the article does not explicitly say so. Would some knowledgeable editor kindly clarify the point, as I've suggested, either in the lede or at the first mention of L-cysteine? J. D. Crutchfield &#124; Talk 21:05, 21 January 2016 (UTC)

Assessment comment
Substituted at 12:37, 29 April 2016 (UTC)

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History of cysteine and cystine
The part on cysteine's history is labeled as incomplete. I have found literature regarding this topic, for instance: https://doi.org/10.1016/S0065-3233(08)60140-0 However, every literature I have come across all have combined descriptions of the history of cysteine and cystine. I also find doing so rather logical, as forcedly separating the two will inevitablely lead to an incomplete view of the subject. Thus, I recommend that we redirect the history section of cysteine into that of cystine, and I shall make additions regarding the history of both there. Pygos (talk) 07:07, 12 May 2024 (UTC)
 * Support. --Smokefoot (talk) 13:07, 12 May 2024 (UTC)

Semiessential
Where in the given reference is it specified that cysteine is "semiessential"? Reading it as a lay person I don't understand. Is this fact in the given reference? Danuthaiduc (talk) 20:56, 12 May 2024 (UTC)