Proteins which run high on SDS-PAGE

[bmans at scientia.up.ac.za]

>   at332 at FreeNet.Carleton.CA (Matt Parker) wrote:
>->      Hi! We are studying a protein of 33 kDa, which consistently runs
>->as about 39 kDa on SDS-PAGE (after boiling 3 mins in SDS buffer). We also
>->are studying a fragment of this protein, of about 19 kDa, which runs at
>->about 25 kDa. Does anybody have any clues as to why this is going on?



Hi there,

If your protein of interest has a lot of disulphide bonds it tends to be very 
compact when its not denatured. Denaturing the protein folds it open ( 3 min. 
in SDS ) and that reduces its mobility on a SDS-PAGE gel. A classic example is 
BSA which when denatured runs at 67 kDa ( its true MM ), but under denaturing 
conditions runs at 55 kDa. A big difference, especially if you use molecular 
markers to determine MM.


Ben