If you are preparing the calf thymus DNA from fibres, they are quite
difficult to rehydrate and are also very much contaminated with proteins
(and who knows what else). When I did this a few years ago, I had to use a
sonicator to clarify the solution, and then try to clean the stuff up by
phenol extraction, etc. I wouldn't trust the UV data too much until you
have the solution clarified since there will be a lot of scattering in the
suspension.
On the other hand, Invitrogen sells a fairly pure calf thymus solution at 10
mg/mL and it's fairly cheap (something like $100 for 5 mL); wouldn't this be
concentrated enough for your purposes?
Gregory
"Aaron Engelhart" <aaron.engelhart at gmail.com> wrote in message
news:afd496b4.0408230123.33877bd6 at posting.google.com...
> We do some work with calf thymus DNA at high concentrations (3-7
> millimolar) in milliliter quantities for spectrophotometry/transient
> absorption spectroscopy purposes. One problem is that it seems to be
> fairly cloudy above the millimolar level. This is the cheapest source
> of DNA, so I like to use it for obvious reasons before doing
> experiments on synthetic oligos or polyG-polyC, etc, but the
> cloudiness is a problem. I have done some work with phenol extraction,
> which seems to help a bit, but with significant product loss. Every
> time I do a phenol extraction, there is a bit of whitish gunk at the
> interface. I don't understand the mechanics of this completely, or
> exactly what it is. There's some obvious product loss from leaving a
> bit of the supernatant behind to avoid taking up the impurity, but my
> understanding is that the dsDNA stays in the aqeuous phase and the
> proteins go into the organic phase. A260/280 ratio looks fine (and
> unchanged!) before and after extraction. Does anyone have a good way
> to clear up CTDNA/know what this is? TIA,
>> Aaron
