Time to start digging in the archives. Try looking at work by Fran
Jurnak in 1986 (J. Cryst. Growth 76, 577) and Bill Ray's work in 1985
(Analytical Biochem 146, 307), and then the works that cite them. I
thought this was common knowledge, but I guess it goes in phases.
Aging of poly(oligo)-oxyethylene-based compounds is well known in the
surfactant field as it changes the chemical properties of common
detergents (Brij, Triton, C10E6, etc.), not only by adding aldehydes
and carboxylates to the system, but also by increasing metal binding.
It is a sobering sight to see old PEG cross-link your 3-month old
crystal: the damn thing wouldn't dissolve after 2 hours in plain
buffer, but when I poked it with a glass fiber, the protein oozed out
like the center of a cherry cordial, leaving a sad looking deflated
shell of a crystal.
Cheers,
Michael
****************************************************************
R. Michael Garavito, Ph.D.
Professor of Biochemistry & Molecular Biology
513 Biochemistry Bldg.
Michigan State University
East Lansing, MI 48824-1319
Office: (517) 355-9724 Lab: (517) 353-9125
FAX: (517) 353-9334 Email: [email protected]
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On Aug 24, 2011, at 5:21 PM, Frank von Delft wrote:
And now, .... does anybody know of systematic data indicating how
consistently all this matters?
phx
On 24/08/2011 21:45, Prince, D Bryan wrote:
For those of us truly controlling types :), I used to make the PEG
solutions and filter them over a Bio-Rad resin that filtered out
all the
junk added to stabilize the PEG solution. Then, of course I had to
freeze all my PEG solutions in aliquots, or wrap them in foil and
store
at 4C in the dark. This would take several days, depending on the
FW of
the PEG. If you are really sensitive about what is in your PEG
solutions, try GC-grade PEG's. The FW profile is much more restricted
around the reported value (i.e. PEG 3350 molecular biology grade
has a
broad peak centered on Mr=3350. PEG 3350 GC-grade has a much tighter
peak profile.) Back before you could buy Crystal Screen I, II or
HT, you
had to make the stock solutions, then make the screen. But at least
when
you did that, you had all the stocks. Now, I just buy pre-made
solutions, and keep them in a drawer with a date opened written on
the
bottle. Isn't progress grand? :)
Bryan
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-----Original Message-----
From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of
Jacob Keller
Sent: Wednesday, August 24, 2011 3:18 PM
To: [email protected]
Subject: [ccp4bb] Aging PEGs
A while ago I measured the pH's of old and new PEGs and found them
very different, and internally attributed all "old vs new PEG issues"
to pH. Upon reflection, this seems too simplistic. Are there other
known mechanisms of crystallization capacities of PEGs of various
ages?
Jacob Keller
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
cel: 773.608.9185
email: [email protected]
*******************************************
