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What cause "downshift" in SDS-PAGE?


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#1 kingswill

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Posted 09 January 2011 - 07:44 PM

There's a protein sample. You splite it into two and subject them to two treatment (presumably 1 control treatment and 1 testing treatment). After that you denature it and run SDS-PAGE. You find that the testing treatment "downshift" the protein, i.e. protein migrate faster than the control. What is/are the possible causes of this?

Everybody knows the most obvious one is phosphatase (or dephosphrylation). I just wanna if there's any possbile mechanism to cause this observation.

#2 ElHo

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Posted 10 January 2011 - 01:35 AM

Actually itīs phosphorylation, not dephosphorylation that causes proteins to migrate faster.

#3 kingswill

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Posted 10 January 2011 - 06:13 AM

Actually itīs phosphorylation, not dephosphorylation that causes proteins to migrate faster.


not to my understanding. Phosphorylation should cause a upshifted band.

#4 mdfenko

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Posted 10 January 2011 - 10:44 AM

deglycosylation, demethylation, delipidation...

phosphorylation will add very little to molecular weight but will increase negative charge on molecule (even in the presence of sds). you can enhance the downshift caused by phosphorylation by running the protein on urea-page.

Edited by mdfenko, 10 January 2011 - 10:47 AM.

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#5 rkay447

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Posted 10 January 2011 - 12:42 PM

I've actually seen both and, like everything else in science, there is no 100% rule. Some proteins will upshift or run slower with the phosphate while others will downshift or run faster with the phosphate. Generally it is thought that a phosphorylated protein will run slower and be the upshifted band but again, not always. For example, phosphorylated MCM2 runs faster and results in a down-shifted band while phosphorylated cyclin B runs slower.

#6 Prep!

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Posted 24 January 2011 - 07:49 PM

what is the testing treatment???
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