Basic question about PMSF

[Dennis]

On 2006-12-14 17:42:43 -0500, Dennis said:

> On 2006-12-13 12:03:47 -0500, "Breslauer" <breslauer1981 At gmail.com> said:
> 
>> 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?).
>> 
>> Thans for any clue
>> 
>> Julio
> 
> You are alkylating at least some protein and increasing its 
> hydrophobicity, so a precipitate is not surprising.
> 
> Why on earth are you adding PMSF to a protein extract?  The common use 
> of PMSF is to add it to a water solution to alkylate and inactivate 
> RNAses.

OOps, I was thinking of TPCK.  Yes, PMSF would be useful to inhibit 
proteases, but it is a rather nondiscriminate alkylator and could cause 
precipitation.
>