Tim, Not really. Fo's can be viewed as having 3 parts. 1) F from our modeled structure, 2) F from what we can't model. This can be bulk solvent, partial or multiple occupancies in low resolution structures, thermal anisotropy , etc. 3) F from random errors in measuring data. The first F is what we deal with. The third F we can minimize by collecting high quality data. The second F is usually crystal/space group dependent. It arises from crystallization conditions, crystal morphology and intermolecular contacts. Data from isomorphic crystals should have similar second F's so map (from first F's) is cleaner.
Doug -----Original Message----- From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Tim Gruene Sent: Wednesday, June 17, 2009 4:39 PM To: [email protected] Subject: Re: [ccp4bb] Difference Map images > I know that sometimes Fo(complex)-Fo(apo) cannot be done because of > nonisomorphism. We've had a lot of success with this with the dioxygenases > because there is no large scale alteration in the active site. As for the > technique itself, Brian Matthews drilled this into me when I was a postdoc > in his lab. Wouldn't - in the case of non-isomorphsim - a molecular replacement with the apo-form come closest to a Fo(complex)-Fo(apo) map? Just a thought. Tim
