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Hi Jacob, An additional technique to identify sodium is microPIXE, which can be used for elemental mapping. I'm not sure if the sulfur signal would be strong enough to be quantitative. A ref: https://www.cell.com/structure/pdf/S0969-2126(00)88335-5.pdf Hope that helps, Sarah Sarah EJ Bowman, PhD Associate Research Scientist, Hauptman-Woodward Medical Research Institute Director, High-Throughput Crystallization Screening Center Research Associate Professor, Department of Biochemistry, University at Buffalo Research Webpage<https://hwi.buffalo.edu/scientist-directory/sbowman/> www.getacrystal.org<http://www.getacrystal.org> [log in to unmask]<mailto:[log in to unmask]> From: CCP4 bulletin board <[log in to unmask]> on behalf of Artem Evdokimov <[log in to unmask]> Reply-To: Artem Evdokimov <[log in to unmask]> Date: Sunday, November 3, 2019 at 9:20 PM To: "[log in to unmask]" <[log in to unmask]> Subject: Re: Sodium Ion Binding? Hi Jacob Not the easiest task... Based on past experience your major issue will be the incredible abundance of sodium ions in everything. So assuming you have high quality sodium free solutions and are willing to work exclusively in plastic, quartz or fused silica - here are a few thoughts: 1. Na-22 isotope binding. An oldie but goodie. 2. Sodium-reactive dye equilibrium (see e.g. reference I put at the end) 3. Flame or ion coupled plasma spectroscopy. Very nice to do given the marvellous sodium band. 4. Sodium selective glass electrode (requires more solution of your analyte than the other methods) Overall the key component to these methods is your ability to displace the sodium with something else prior to measuring the effect of titration the ion back. Isotopic Na is easier in this regard - but at a cost... Hope this helps. Artem https://bmcresnotes.biomedcentral.com/articles/10.1186/1756-0500-6-556 https://www.google.com/url?sa=t&source=web&rct=j&url=http://clinchem.aaccjnls.org/content/clinchem/24/4/580.full.pdf&ved=2ahUKEwis5KL_vM_lAhXCmuAKHY2cAVQQFjAFegQIARAB&usg=AOvVaw0Yhz23Yr_ulB85MDQspIFl&cshid=1572833723049 On Sun, Nov 3, 2019, 20:41 Keller, Jacob <[log in to unmask]<mailto:[log in to unmask]>> wrote: Dear Crystallographers, Does anyone know of a good biophysical way to identify or quantify sodium ion binding to a protein, besides crystallography and ITC? Is this possible with SPR, perhaps? Mass spec? Gel shifts? Examples would be greatly appreciated! All the best, Jacob Keller +++++++++++++++++++++++++++++++++++++++++++++++++ Jacob Pearson Keller Research Scientist / Looger Lab HHMI Janelia Research Campus 19700 Helix Dr, Ashburn, VA 20147 Desk: (571)209-4000 x3159 Cell: (301)592-7004 +++++++++++++++++++++++++++++++++++++++++++++++++ The content of this email is confidential and intended for the recipient specified in message only. It is strictly forbidden to share any part of this message with any third party, without a written consent of the sender. If you received this message by mistake, please reply to this message and follow with its deletion, so that we can ensure such a mistake does not occur in the future. ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1