Small proteins are underestimated on SDS-PAGE?

[Lee, Ji Hyun]

When much proteins of large molecular weight co-exist, do proteins of

small molecular weights(6500 dalton) tend to be underestimated on
SDS-PAGE? 
In other words, compared to their absolute contents their bands look
light in

mixture of very much of other proteins but when only they are SDS-PAGEd

their bands look dark despite of the same contents.


Is it possible? 

Any comments and any reference will be appreciated.



Thank you.