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Author: Subject: Disulphide linkages. R - S - S - R
vimal
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[*] posted on 1-2-2005 at 17:54
Disulphide linkages. R - S - S - R


they are mostly found in proteins right? esp. Insulin. Now, the question says:

In the analysis of insulin, attempting to reduce the chain length, the disulphide linkages are first broken down.
write the products obtained when the disulphide linkage is treated with:
HS-CH2-CH2-OH
HCOOOH performic acid




Vimal
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runlabrun
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[*] posted on 1-2-2005 at 21:19


found this in a few secs on google dont know if its what you want or not....

http://www.med.unibs.it/~marchesi/pps97/course/insulin/sange...

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JohnWW
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[*] posted on 2-2-2005 at 01:29


The only natural amino-acid, of the 23 natural ones, containing a disulfide linkage R-CH2-S-S-CH2-R is cystine, HOOC-CH(NH2)-CH2-S-S-CH2-CH(NH2)-COOH. It is reversibly reducible to 2 molecules of cysteine, HOOC-CH(NH2)-CH2-SH, containing -SH groups.

The disulfide linkages in cystine units are important in determining the overall shapes of protein molecules, because their cross-linking of chains of amino-acid units results in 3-dimensonal rigidity. This is why cystine is most common in "hard" proteins such as keratin, as in hair, nails, horns, and skin.

There is also a natural S-S containing carboxylic acid, lipoic acid, cyclo-(-S-S-CH2-CH2-CH-)-(CH2)4-COOH, which is an important cofactor in biological oxidations. It is reversibly reducible to dihydrolipoic acid, HS-CH2-CH2-CH-(CH2)4-COOH.

In nature, the disulfide linkage in the above compounds is not oxidized, but is reduced to two -HS groups. Treatment with an oxidant like performic acid would not be similar to any natural biochemical reaction. The reaction products would probably be initially two molecules of a sulfoxide containing tetravalent sulfur, -CH2-SH=O, and further oxidation would probably result in a substituted sulfurous acid, -CH2-S(OH)=O, and then a sulfonic acid, -CH2-SO2-OH. Treatment with a mixed thiol and alcohol like HS-CH2-CH2-OH would most likely result in an ester and/or thioester.

[Edited on 2-2-2005 by JohnWW]
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