Basic question about PMSF

[Jose de las Heras]

"Bean Long" <ben.long At yourfinger.anu.edu.au> wrote in message 
news:4587575e$1 At clarion.carno.net.au...
> Dr Engelbert Buxbaum wrote:
>> Breslauer wrote:
>>
>>> Listen,
>>> is it normal that when adding PMSF (250mM solution in MeOH) to cell
>>> free extract from E.coli (broked by sonication and spinned 12000g for
>>> 30min) to the final concentration of 0,5mM buffer becomes cloudly and
>>> st become to precipitate (probably protein?).
>>
>> No. At this concentration PMSF should not precipitate proteins, nor
>> should it precipitate itself (provided that excessively high local
>> concentrations are avoided during mixing).
>
> I was surprised to hear you had a stock of 250 mM.  I didn't think PMSF, 
> even in methanol, was that soluble.  I usually make up a 170 mM stock in 
> isopropanol.  Having said that, I'm sure that wouldn't be the problem. You 
> may want to check one of the original reports on using PMSF as a protease 
> inhibitor:


It dissolves well at 200mM in isopropanol, in my experience.

Jose