Achim Recktenwald, PhD achim at
Fri Sep 27 14:05:49 EST 1996

Jussi Kankare wrote:
> Dear Netters,
> I'm trying to crystallize a protein and would therefore like
> to have my sample as homogeneous as possible. However when the
> purity of the sample is checked with SDS-page the gel shows a
> major and small minor band just beneath the major one. I have
> not purified the sample myself but the persons who have done
> the work claim that the sample is pure but the protein just has
> the property that it shows two bands in SDS-page ?!? I would naturally
> think that this means that the sample is NOT homogeneous. What could
> cause this sort behaviour of a protein or is there simply a need for
> repurifying the protein.

The protein/enzyme could be a herteromer composed of several different
If it is a homomer or not a multimeric protein at all, these bands could
be caused by degradation, natural as well as by proteinases present as
impurities. Asp-pro bonds are quite acid labile, the protein could be
nicked over time during storage.

Your protein could be glycosylated or has some other kind of
posttranslational modification. These modifications are usually not 100%


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