Thread: SDS Polyacrylamide Gel Electrophoresis Questions...

My professor assigned some study questions with only vague reading material available to assist, and I'm a bit lost. This lab in Cell/Molec Biology is over the MW of proteins. We ran a standard Gel Electrophoresis with unknown proteins and plotted the data on semi log paper to determine the unknowns..

Anyways, here's the questions I'm stuck on:

"The migration rate of glutamate dehydrogenate is similar to the migration rate of Beta-amylase during SDS PGE. Yet the native molecular weight of glutamate dehydrogenate is 330 kDa and that of Beta-Amylase is 206 kDa. Explain.".

And..

"A glycoprotein consisting of a single polypeptide chain and over 40% (by weight) of N-acetylglucosamine, mannose and sialic acid was found to have a native molecular weight of 75,000 by several analytical methods. However, analysis by SDS polyacrylamide gel electrophoresis gave molecular weight of 100,000. Explain.".

I'm not asking for the answers but I would like it if someone were to point me in the right direction with this, very frustrating.

I understand the basic concept and the different ways of breaking apart the protein, so I know how certain things can alter the results (That is, produce different bands for the same protein, etc..). I'm not completely new to this!

Thank you for anyone stopping to take the time to help, I've skimmed through this forum multiple times (Many just from googling) and have found it to be an excellent source of information!

To the first question -

Here's a hint, think about the components of the sample buffer.... are there any components in there that may be capable of reducing disulphide bonds.... what might this do to the native protein?

Then, looking at the relative MWs of glutamate dehydrogenase and beta-amylase, may give go some clue as to what is going on....

Best wishes,

Tri~