Dear Dean, You have already received excellent insight into radiation effects on metals. From personal experience, it doesn't take long for the metal occupancy to go down to 80%. Of course it is not anywhere near "disappearing" but then again, we don't know the details of your data collection and of how disappeared are your disappeared metals.
I will only add that you can use modern approaches to data collection to minimize the adverse effects of radiation. 1. Do not chase the highest resolution and try to get what is enough to make your enzymologic statements valid. I.e. use less dose. 2. If your crystals diffract poorly, consider using several crystals to merge few sets of underexposed data. 3. For each crystal, use some sort of grid scanning (we call it rastering) to estimate the crystal quality. It is implemented on many beamlines worldwide. I will insert a shameless plug here and others can follow the suite... See Hilgart et al., pages 717-722 here: http://journals.iucr.org/s/issues/2011/05/00/issconts.html 4. Select the better diffracting regions of the crystal and use "vector" or "helical" data collection whereby your crystal is being translated along the specified vector as data is being collected. This feature is also implemented on number of beamlines, including ours (see the reference above). All these steps are designed for one goal - to spread the total dose over as much diffracting volume as possible and thus minimize the damage. Hope it helps, N. Ruslan Sanishvili (Nukri) Macromolecular Crystallographer GM/CA@APS X-ray Science Division, ANL 9700 S. Cass Ave. Lemont, IL 60439 Tel: (630)252-0665 Fax: (630)252-0667 rsanishv...@anl.gov ________________________________ From: CCP4 bulletin board [CCP4BB@jiscmail.ac.uk] on behalf of Dean Derbyshire [dean.derbysh...@medivir.com] Sent: Wednesday, April 30, 2014 5:33 AM To: CCP4BB@jiscmail.ac.uk Subject: [ccp4bb] metals disapear Hi all, Has anyone experienced catalytic metal ions disappearing during data collection ? If so, is there a way of preventing it? D. Dean Derbyshire Senior Research Scientist [cid:image001.jpg@01CF6470.5FA976D0] Box 1086 SE-141 22 Huddinge SWEDEN Visit: Lunastigen 7 Direct: +46 8 54683219 www.medivir.com<http://www.medivir.com> -------------------------------------------------------------------------- This transmission is intended for the person to whom or the entity to which it is addressed and may contain information that is privileged, confidential and exempt from disclosure under applicable law. If you are not the intended recipient, please be notified that any dissemination, distribution or copying is strictly prohibited. If you have received this transmission in error, please notify us immediately. Thank you for your cooperation.
