Activated charcoal in DNA preparation ??

A.Marchant marchaa at
Tue Feb 28 22:45:59 EST 1995

Annoyingly for molecular geneticists, many organisms contain chemicals
other than nucleic acid.

Inhibition of reactions (PCR especially, restriction enzyme
digestion, etc) is often a problem, especially when the preparation is one
of the relatively 'quick and easy' methods (such as just grinding the
sample up in buffer, and spinning down the solid stuff) - but some
organisms have reaction-inhibiting chemicals which persist through much
more elaborate preparation procedures.

Pigments also persist in the nucleic acid preparations from some things,
and, even if they don't interfere with reactions directly, they often get
the blame when things go wrong, and much time is wasted trying to remove them.

I just had an idea, and, rather than trying it out myself, I thought I'd
submit it to the greater collective wisdom:

How about adding activated charcoal to the sample when it is initially
ground up (irrespective of the particular nucleic acid purification recipe)?
This may absorb many unwanted chemical species, and it would get removed
from the preparation in the same centrifugation step that removes solid
debris from the homogenate.

A question is, would it also remove nucleic acids?  I believe that
activated charcoal acts by some sort of 'physical' trapping of molecules
in its pores - would nucleic acid molecules be absorbed, or not?  If not,
then activated charcoal would act much like the size-exclusion resins
(sephadex, etc).  Also, are these PCR inhibitors (etc) believed to be
small or big molecules?  Humic acids (in the PCR-from-old-things world) gets a
lot of flack - I believe that they are polymers, and so this probably
wouldn't get rid of them.

Do people have any ideas?  Has this been tried?  

Adam Marchant
marchaa at

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