Re: How does egg albumen denature using copper (II) sulphate

Hi Samantha,

I'm sorry that it has taken so long to answer your question, but I hope that you will still find the answer useful. What we call egg albumen is a mixture of several proteins and other compounds that constitute egg whites. As you can see from this discussion of albumen protein chememistry, egg albumen is mostly water (~89%) and protein (~10%). More than half of the protein in egg albumen (63%) is represented by the the proteins ovalbumin and conalbumin. When we talk about denaturation of the egg albumen, we're talking about the unfolding of these albumen proteins from their native, folded state. This is discussed at great length in the link I provided above as well as here on the MadSci Network, so I won't discuss it, except to point out that all of these proteins contain significant numbers of Cysteine residues, which are sulfhydryl (-SH) containing residues crucial in establishing and maintaining proper protein structures. The sulfhydryl groups of two Cysteine residues can form a covalent disulfide bond (-S-S-, a Cystine), which holds two distant sections of protein in close proximity.

Now, your question dealt specifically with the denaturation of albumen proteins by copper sulfate, a potent toxin, with a variety of toxic, teratogenic, mutagentic and carcinogenic effects, that is used as a fungicide. The action of copper sulfate in protein denaturation derives from its ability to disrupt disulfide Cystine bonds, binding to individual sulfhydryl groups. When this happens, the sections of the protein which were held in close proximity by the Cystine bond are free to move apart, which usually allows water molecules to enter the core of the protein, which leads to further disruptions, etc...

So, there you have it. Copper sulfate denatures egg albumen by disrupting Cystine bonds in the various albumen proteins, most of which are albumins. This phenomenon has been the subject of considerable study and application. For example, take a look at the abstract for the paper I have referenced below, which describes a system for controlling the clevage of Cystine bonds in bovine serum albumin.

Kumar N, Kella D, Kinsella JE. (1985) A method for the controlled cleavage of disulfide bonds in proteins in the absence of denaturants. Biochem & Biophys Methods 11(4-5):251-63.