Detergents function??

nestgrp at earthlink.net nestgrp at earthlink.net
Wed Mar 5 19:54:40 EST 1997


Balwi <M.Albalwi at sheffield.ac.uk> wrote:

>Hi everybody,


>We hear a lot about detergent particulay in molecular biology. Is any 
>body know why some prefer SDS, Tween 20 or Triton X-100. If you think 
>you know scientific answer why SDS or Tween 20 or Triton X-100 prefer 
>than each other please e-mail me.

Balwi:

This question could fill an entire textbook!!  But, let me try to give
you a few highlights:

1)  Detergents can be either ionic (SDS, deoxycholate) or non-ionic
(Tween, Triton, Digitonin)  which can greatly affect your application
or purification.  For example, one uses SDS for PAGE gels to impart a
negative charge to proteins creating an equivalent charge to mass
ratio for all proteins in a mixture.  If you want to use ion exchange
chromatography for either proteins or DNA, a non-ionic detergent such
as Tween or Triton would be a better choice.

2)  Each detergent has a critical micellization concentration (CMC)
which is defined as the concentration above which micelles are formed.
The CMC may determine the concentration of detergent needed to perform
a specific solubilization.  For example, the CMC of SDS is 0.23% (w/v)
while the CMC of Triton X-100 is 0.021%.  Therefore, a lower
concentration of Triton X-100 could be used to perform a task needing
a higher SDS concentration.

3)  Does the detergent precipitate under cold temperatures?  SDS does
but Triton and Tween do not.  Therefore, SDS is the prefered detergent
in alkaline lysis for DNA preps.  Triton and Tween could just as
easily be used to lyse E. coli but one would not be able to get rid of
it as easily as SDS (which is precipitated with cell debris and
genomic DNA after the alkaline lysis).  

NOTE:  As stated above, SDS is an ionic detergent.  If you use an
ion-exchange DNA purification kit for your plasmid preps you need to
be very careful that you remove as much of the SDS from your lysate as
possible.  If you have residual SDS in your supernatant and  apply it
to the ion-exchange cartridge you will DRAMATICALLY reduce your yield.
SDS will bind to these cartridges and preclude the binding of DNA
(which will just pass through the column leaving you with another
100-500 ml culture to grow, another alkaline lysis and purification=
at least 24 hrs)  BE CAREFUL AT THIS STEP and you can save yourself
time and money!! 

Hope this answers some of your questions. 

Regards,

John





**********************************
John K. Troyer, Ph.D.
The Nest Group, Inc.
nestgrp at earthlink.net
http://world.std.com/~nestgrp
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