I recently did a lab on protein precipitation and we used various reagents to precipitate the proteins from a standard protein solution. When I added copper sulphate solution and lead acetate solution, I got a white precipitate for both. I know that heavy metal ions are supposed to precipitate proteins out of solution but I can’t seem to find the theory behind it. Does anyone know how these ions precipitate proteins?……thanks
Things like Cu, Pb, and Hg bind strongly to the sulfurs of cysteines. They can sometimes bind to Histidines or the sidechains of Aspartates and Glutamates. They will sometimes displace structurally important metals, but the heavy metals are large (relative to things like Na or K or even Zn) and often dislocate parts of the protein molecule. Eventually, it can lead to denaturation and precipitation.