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The PEG could also be the problem, so you can mix your stock solutions by the method described below and end up with the same result as soon as you add the PEG. See: Frances Jurnak: Effect of chemical impurities in polyethylene glycol on macromolecular crystallization Journal of Crystal Growth Volume 76, Issue 3, 2 August 1986, Pages 577-582 Enrico. On Tue, 27 Sep 2011 18:43:09 +0200, Roger Rowlett <[log in to unmask]> wrote: > Imidazole is basic. If you mix it directly with zinc salts you will get > zinc > hydroxide. Most screens are prepared by mixing stock solutions. In your > case > I would make up the screen from 1 M imidazole, pH 7.2, 1 M ZnSO4, and 50% > PEG-4000. Add the PEG last. This should work. You may or may not need > this > specific salt or buffer to get crystals, and could swap them out or > change > concentration as required. 50 mM buffer may not be sufficient to control > condition pH depending on the protein storage buffer composition. > > Roger Rowlett > On Sep 27, 2011 11:56 AM, "Browning Christopher" < > [log in to unmask]> wrote: >> Dear All, >> >> My question might be a bit out of place, but perhaps someone can help. > I've screened my protein in the Nuc-Pro screen from Molecular Dimensions > and > found some crystals in condition B10. They seem to be protein crystals as > they are not highly optically active and look different to salt > crystals. So > condition B10 consist of 10% PEG 4K, 50mM Imidazole pH 7.2, 20mM Zinc > sulfate. In the screen, this condition is perfectly clear, but when I try > and make my own screen, the whole solution turns white. Apparently, Zinc > sulfate/Imidazole can be used for staining SDS-gels, but that does not > really help my a lot. Does anybody have an idea how I might be able to > keep > everything in solution, seeing that the MD guys managed somehow...... > I'm a > bit desperate as I don't have many hits for this protein. >> >> Cheers, >> >> Chris B >> >> -- >> Dr. Christopher Browning >> Post-Doctor to Prof. Petr Leiman >> EPFL >> BSP-416 >> 1015 Lausanne >> Tel: 0041 (0) 02 16 93 04 40 -- Enrico A. Stura D.Phil. (Oxon) , Tel: 33 (0)1 69 08 4302 Office Room 19, Bat.152, Tel: 33 (0)1 69 08 9449 Lab LTMB, SIMOPRO, IBiTec-S, CE Saclay, 91191 Gif-sur-Yvette, FRANCE http://www-dsv.cea.fr/en/institutes/institute-of-biology-and-technology-saclay-ibitec-s/unites-de-recherche/department-of-molecular-engineering-of-proteins-simopro/molecular-toxinology-and-biotechnology-laboratory-ltmb/crystallogenesis-e.-stura http://www.chem.gla.ac.uk/protein/mirror/stura/index2.html e-mail: [log in to unmask] Fax: 33 (0)1 69 08 90 71