So we want to answer the following question how do we determine the position of the sulfide bonds in that protein that contains these disulfide bridges. So we have to follow three different steps. And what we use is a special process known as diagonal electrophoresis which is basically two different applications of the gel electrophoresis process as we'll see in just a moment. So let's suppose this is the protein and in the protein we have these two polypeptides and they are connected to one another at two locations by disulfide bond. So this is disulfide bond number one and disulfide bond number two. Now what we want to do initially is we want to take this protein and expose it to some type of proteolytic enzyme.