Question about quantitating western blots.

Michael L. Sullivan mlsulliv at
Fri Dec 7 14:31:16 EST 2001

In my experience, the signals can be vary non-linear, and dependent on a
number of factors, including the nature of the Ab, so a 2-fold difference
in signal might not mean a 2 fold difference in protein.  If you don't want
to run a standard curve, I think you may at least have to run various
amounts of the samples you wish to compare.  Then you'd be able to say
something like 5 ug of total protein on day 2 had the same signal as 10 ug
of total protein on day 1, so day 2 had 2-fold more of your protein of
interest.  However, if you just loaded 10 ug of each sample and saw signals
that were 2-fold different, I don't think you could draw the conclusion
that there was 2-fold more protein.  Does that make sense?

Hope this helps.


>Thanks for the input, it's greatly appreciated!  One more question, if
>what we really want to know is the relative amount of protein between
>samples, is a standard curve on the gel necessary? We arent interested in
>absolute amounts of protein in each sample. ie if we scan the blot and
>quantitate the bands, can we say there is 2 fold more protein on day 2
>than on day 1 for example?
>Or is the standard curve necessary to be certain that the measured pixel
>intensity of the samples falls within the linear range of the scan?
>Thanks again for the help!

Michael L. Sullivan, Ph.D

U.S. Dairy Forage Research Center
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Madison WI, 53706

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