Talk:Disulfide

Shouldn't the first paragraph state that they're a part of tertiary and quaternary structure, not secondary and tertiary? Thedudester09 (talk) 18:26, 8 June 2020 (UTC)

Can disulfides bind to metals, as thiols do? Stonemason89 (talk) 20:13, 26 November 2010 (UTC)
 * Complicated and depends on how you ask the question and what you are after. You probably do not mean the question the way that you phrased it.  A lot depends on how you think that thiols "bind to metals"?--Smokefoot (talk) 01:30, 27 November 2010 (UTC)

Merger proposal
The following seems too technical for inclusion in this article. --Smokefoot (talk) 00:38, 22 October 2018 (UTC) This page and Disulfide bond appear to be fairly obvious content forks of one another and should be merged. --Project Osprey (talk) 12:39, 23 September 2015 (UTC)
 * Seems noncontroversial. Thanks for doing this.  --Smokefoot (talk) 17:04, 23 September 2015 (UTC)
 * agreed, good idea V8rik (talk) 17:50, 23 September 2015 (UTC)
 * Done. I've had to reorganize things a little and the whole page still needs work, there's a great lack of in-line citations. --Project Osprey (talk) 08:50, 24 September 2015 (UTC)

Predicting disulfide abundance
The number of ways i in which p disulfide bonds can be formed from n cysteine residues present in a protein is given by the formula


 * $$i = \frac{n!}{(n-2p)!\, p!\, 2^{p}}$$

Here,
 * i is the number of different disulfide bond isomers or connectivities possible.
 * n is the number of cysteines present in the protein molecule.
 * p is the number of disulphide bonds that are formed (hence 2p is less than or equal to n).

The above formula is the most general relation which can be used to calculate the number of possible disulfide bond isomers (or connectivities) when n is either even or odd, and when all or only some of the cysteines are involved in the formation of disulfide bonds.

However, many of the naturally occurring proteins that have disulfide bonds possess an even number of cysteines with all of the cysteines participating in the formation of disulfide bonds. For this specific case, n is an even number and p is equal to $n⁄2$. Substituting the value of p, the above formula for the possible number of disulfide bond connectivities simplifies to:


 * $$\begin{align}

i &= \frac{n!}{(n-2p)! \, p!\, 2^{p}} \\ &= \frac{n!}{ \left(n-2\left(\frac{n}{2}\right)\right)! \, { \left(\frac{n}{2}\right) }! \, {2^{ \frac{n}{2} } } } \\ &= \frac{n!}{ { \left(\frac{n}{2}\right) }! \, {2^{ \frac{n}{2} } } } \end{align}$$

For this particular case (n is even and all cysteines form disulfide bonds), a formula which is more easier to remember is given by:


 * $$i = (n-1)\, (n-3)\, (n-5)\, \cdots 1$$

Both of the above relations hold good for the proteins which have an even number of cysteines and all the cysteines are involved in the formation of disulfide bonds. Both of the above formulae are derived using the same logic and essentially represent a simplification of the same starting formula.

As a specific example for the above case, an eight-cysteine protein such as ribonuclease A can form 105 different four-disulfide species when all the cysteines are involved in the formation of disulfide bonds. Here n = 8 and p = 4.

So, here

i = (8-1)\, (8-3)\, (8-5)\, (8-7) = 7 \cdot 5 \cdot 3 \cdot 1 = 105 $$

Only one of the 105 possible isomers is the native disulfide species. Isomerases have been identified that catalyze the interconversion of disulfide species, accelerating the formation of the native disulfide species.

Disulfide species that have only native disulfide bonds (but not all of them) are denoted by "des" followed by the lacking native disulfide bond(s) in square brackets. For example, the des[40–95] disulfide species has all the native disulfide bonds except that between cysteines 40 and 95. Disulfide species that lack one native disulfide bond are frequently folded, in particular, if the missing disulfide bond is exposed to solvent in the folded, native protein.

In order to analyze the structure of proteins, it is often necessary to break disulfide bonds. This reduction of disulfide bonds can be accomplished by treatment with 2-mercaptoethanol, dithiothreitol, or tris(2-carboxyethyl)phosphine.

Chemistry
For some unknown reason, Editors are writing rubbish as if it was fact. The section on Inorganic Disulfides claims "Sulfur is usually assigned to the reduced oxidation number -2...". Aside from the fact that it is the (theoretical, hypothetical) oxidation number that is assigned to the element (and not the other way around), it just. isn't. true. Sulfur commonly can be found in the 0, -2, and +6 formal oxidation states in nature. Millions of tonnes of gypsum are mined every year, gypsum is Calcium sulfate (+6). Pyrite (Fool's Gold) is the most common of the sulfide minerals, and sulfur's formal oxidation number is -1 there (Fe is NOT commonly found in the +4 Ox. State which is what would be required if S was in the (not so common) -2 state. I could go on, and on, and on. I'm not even sure (citation required) that in organic chemistry the -2 state is more common that the +6 state (in terms of industrial organic chemicals).174.130.70.61 (talk) 17:55, 5 April 2020 (UTC)