[Mr.A]

That is a fact,there are four types of bonds in complex proteins.

I learned , in the denaturing of proteins , disulphide bonds can not be broken at any case.It was taught by one teacher.Another teacher said that it is possible to denature the protein by providing a temperature of 60 degrees Celsius for a period of more than 10 minutes.I got to know,when the protein is totally denatured 'only the primary structure of protein is left.So,there must be only peptide bonds.That means disulphide bonds are also can be broken in the denaturing of proteins.Please explain the interconnection between these facts.

[Babcock_Hall]

Can you list the four types of bonds you mean?  One, not every protein has disulfide bonds.  Some do (ribonuclease A, insulin, chymotrypsin, and IgG), but many do not.  Two, it is possible to break disulfide bonds with reducing agents, such as 2-mercaptoethanol or dithiothreitol.  These chemicals help to denature proteins that have disulfide bonds, but they stabilize proteins that have cysteine residues in the thiol form.  Three, reagents such as urea and SDS do not break disulfide bonds, but they can denature proteins at sufficiently high concentration.  A protein with its disulfide bonds intact but which has undergone a major conformational change will probably not retain its biological activity.  Four, every protein is different with respect to the temperature at which it denatures.