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We did a study of lactate contamination in PEGs and found millimolar levels in some PEGs: Zhang M, Tanner JJ. Detection of L-lactate in polyethylene glycol solutions confirms the identity of the active-site ligand in a proline dehydrogenase structure. Acta Crystallogr D Biol Crystallogr. 2004 May;60(Pt 5):985-6. PMID: 15103160 Jack > From: Daniel Anderson <[EMAIL PROTECTED]> > Date: Wed, 5 Jul 2006 16:03:56 -0700 (PDT) > To: Mischa Machius <[EMAIL PROTECTED]> > Cc: Bulletin Board CCP4 <[email protected]> > Subject: Re: [ccp4bb]: How to test for PEG contamination? > > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > Hello, everybody, > > I have here Proceedings of the First International Conference on Protein > Crystal Growth from 1985 (when I was younger), published as a special > issue of Journal of Crystal Growth (1986). > > J.Cryst.Growth 76 (1986), 577-582 by Fran Jurnak discusses impurities in > PEG. There's a reference to Ray and Puvathingal, Anal.Biochem. 146 (1985) > 307, discussing how to purify PEG (borohydride reduction follwed by > de-ionization). The one time somebody here tried to purify their own PEG, > they measured concentration of the final product by comparison of its > index of refraction to a table of such things that they found somewhere. > > You could measure conductivity of your PEG solution to get a clue how much > ionic stuff is present. > > We have small PEG's in plastic bottles, and they gradually collapse their > containers, I assume by absorbing oxygen. > > (I think) Fluka specifies "percent ash" which is a measure of non-PEG > non-flammable inorganic components. Fluka "microselect" and the gas > chromatography grade PEG4000 from EM (EMD?) work well for us. > > -Dan Anderson > > > > On Wed, 5 Jul 2006, Mischa Machius wrote: > >> *** For details on how to be removed from this list visit the *** >> *** CCP4 home page http://www.ccp4.ac.uk *** >> >> >> Hi y'all - We are trying to figure out how "good" some of our PEGs >> still are and would appreciate if anybody had any advise for a proper >> assay. >> >> Specifically, PEGs, as well as other organics, such as dioxane, >> glycerol, etc., over time accumulate peroxides that are harmful to >> proteins. The good old iodide test (mixing the sample with potassium >> iodide/acetic acid) gives some hints about peroxides in a sample. >> However, I would like to be more quantitative. Essentially, I'd like >> to define a threshold value at which a chemical should be discarded, >> and I'd like to have a reliable test for that. There are quantitative >> kits available that use Fe++/xylenol orange. Here are the questions: >> >> 1. Does anyone actually test their chemicals for peroxides? >> >> 2. What tests would be useful for PEGs, dioxane, glycerol, and the >> likes? >> >> 3. Has anyone bothered to define a threshold for 'good' vs. 'bad'? >> >> 4. Is peroxide formation a problem only for liquid PEGs, or does it >> also happen to a significant degree in solid PEGs? >> >> 5. What is the best storage method for (liquid) PEGs? Does storage at >> 4°C or -20°C prolong the lifetime? >> >> 6. Any other thoughts? >> >> Many thanks in advance. >> >> Best - MM >> >> ------------------------------------------------------------------------ >> -------- >> Mischa Machius, PhD >> Associate Professor >> UT Southwestern Medical Center at Dallas >> 5323 Harry Hines Blvd.; ND10.214A >> Dallas, TX 75390-8816; U.S.A. >> Tel: +1 214 645 6381 >> Fax: +1 214 645 6353 >> >> >> >
