Hi Stefan, IIRC, a ring at 20Å means that one of the cell edges is at least 20Å long - which might be considered unusually long for a salt crystal - but it's also on the short side for a protein cell edge - how big is your protein?
If there are rings at lower resolution, then maybe these longer edges might be more indicative of protein spherulites, as opposed to salty ones. Can you wash some spherulites in mother liquor and run them on an SDS-PAGE gel? Dave ============================ David C. Briggs PhD Father, Structural Biologist and Sceptic ============================ University of Manchester E-mail: david.c.bri...@manchester.ac.uk ============================ http://manchester.academia.edu/DavidBriggs (v.sensible) http://xtaldave.wordpress.com/ (sensible) http://xtaldave.posterous.com/ (less sensible) Twitter: @xtaldave Skype: DocDCB ============================ On 6 April 2011 11:29, Stefan Münnich <smunn...@vub.ac.be> wrote: > Hi Dave, > > thanks for your reply. Is there any chance of telling whether it is salt or > protein from the diffraction image? > > Stefan > > > On Apr 6, 2011, at 12:16 PM, David Briggs wrote: > >> Hi Stefan, >> >> It looks like a powder diffraction-type image. >> >> http://en.wikipedia.org/wiki/Powder_diffraction >> >> You can imagine that your spherulites are made up of many small >> crystals in random orientations, a bit like a powder - this means that >> rather than getting discrete diffraction spots as you would hope to >> see for a single crystal, you see diffraction rings around the beam >> centre. >> >> HTH, >> >> Dave >> >> ============================ >> David C. Briggs PhD >> Father, Structural Biologist and Sceptic >> ============================ >> University of Manchester E-mail: >> david.c.bri...@manchester.ac.uk >> ============================ >> http://manchester.academia.edu/DavidBriggs (v.sensible) >> http://xtaldave.wordpress.com/ (sensible) >> http://xtaldave.posterous.com/ (less sensible) >> Twitter: @xtaldave >> Skype: DocDCB >> ============================ >> >> >> >> On 6 April 2011 09:32, Stefan Münnich <smunn...@vub.ac.be> wrote: >>> Hey guys, >>> >>> When I collect data from these spherulites/crystals (grown in 0.1 M sodium >>> acetate, 0.1 M MOPS pH 7.5, 12 % (w/v) PEG-8000, protein buffer: 100 mM >>> NaCl, 50 mM HEPES pH 7.5): >>> http://img695.imageshack.us/i/cryst.png/ >>> I get this diffraction pattern: (it's not cryo protected, so there's some >>> ice-rings also) >>> http://img683.imageshack.us/i/diffv.jpg/ >>> >>> It can't be only ice-rings because those are usually starting at something >>> like 3.8 A, whereas I already got one ring directly around the beam center >>> and also one at about 20 A. >>> Has anybody seen anything like that and tell me what it is? >>> >>> Stefan >
