Dear all, in my electron density I can see negative difference density (fo-fc) for the carboxyl groups of some aspartates or glutamates. Assuming that this is a result of partial decarboxylation due to radiation damage, I wanted to refine the occupancies of these carboxyl groups. To this end, I set the occupancy of these atoms to 0.99 in Coot so that they would be picked up by occupancy refinement in phenix.refine (using version 1.4-3). Phenix however just put the value back to one. It looks like the occupancy refinement in phenix is meant for alternative conformations where the sum of the occupancies of the different conformations is 1. How can I make phenix refine partially decarboxylated acidic side chains? It does not seem appropriate to me to make alternative conformations, one with and one without the carboxyl group. That would look funny at my resolution (2.7 Angstrom) and might not fix the problem. Any hints are appreciated. Thank you, Nicole ---- Nicole Bischoff, M. Sc. PhD student in the Gruetter lab Department of Biochemistry University of Zurich Winterthurerstrasse 190 8057 Zurich Switzerland +41 44 635 5556 [email protected]