Talk:Cysteine

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Changed rating to "high" as this amino acid is specifically mentioned in high school/SAT biology prep material - tameeria 19:32, 22 February 2007 (UTC)
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Changed rating to "high" as this amino acid is specifically mentioned in high school/SAT biology prep material - tameeria 19:32, 22 February 2007 (UTC)

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)


Contents

[edit] Hydrophobic vs. hydrophilic

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

What about this? [1]
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)

[edit] 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.

[edit] Pronunciation

Could somebody please add the pronunciation for cysteine?

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

[edit] 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)

[edit] 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)

[edit] 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, β-mercaptoethanol, and TCEP.
  2. Second what does protein purification techniques have to do with sheep?

[edit]

[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)

  • 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)

[edit] 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)