http://bitesizebio.com/580/how-sds-page-works/
This could work. Its literally gel electrophoresis, just with SDS (a detergent to reduce proteins which means to cleave the disulfide bonds)
All this is, its just a method to see how much proteins weigh. and if SDS is in there, then the proteins will separate and you see how much the individual components weigh:
Example: You have an unknown dimer that has a total weight of 200 kDa. This is established when you first ran this protein under PAGE and you see 1 dark band thats next to the comparative 200 kDa.
When you added SDS, it broke apart the disulfide bonds linking the dimer together. Now in that lane of the well, you will see 2 dark bands instead of 1, 1 at say 150 kDa and 1 at 50 kDa. Both of them will be further down the gel since they weigh less than 200 kDa individually. The 50kDa will be the furthest down since it weighs the least.