Which determines mobility?

Keith Leppard Keith.Leppard at warwick.ac.uk
Tue Jul 23 06:42:48 EST 1996

Namjin  Chung <nc1 at acpub.duke.edu> wrote:
> Dear Netters,
> I'm wondering which determines the mobility during SDS-PAGE between 
> voltage and current.  I guess it could be the voltage because the 
> voltage difference between +end and -end makes slope so that proteins on 
> the voltage slope migrate downward.
> One of my clollegues likes to set current constant, and when I plug into 
> his power supply, he complains because it increases the current though 
> voltage is constant.  However, I think as long as the voltage is 
> constant, the mobility would not be changed.  Am I wrong?
> ************************************************************************
> * Namjin Chung                             *                           *
> * Program in Molecular Cancer Biology      * Email: nc1 at acpub.duke.edu *
> * Duke University Medical Center, Box 3345 * Voice: +1 (919) 684-2363  *
> * Durham, NC 27710                         * Fax  : +1 (919) 681-8253  *
> ************************************************************************
The rate of migration of charged species on a gel is determined by the
voltage, not the current, although the two properties are related (V=IR).
When you link two gels to the same 
power pack they are coupled 'in parallel'. With the power pack set at 
constant voltage, the voltage drop across each arm of the parallel circuit
will be the same as the set figure and adding your gel will have no effect
on the one already running. If the setting is constant current, then
adding your gel will take a share of the current and slow the running of 
the other gel.
I hope this helps.

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