Hello Doug,
I understand your arguing, although I do not understand why Fo contains a
contribution from the model(led structure). My idea was only supposed to
be a backup in case the apo-form had not been measuredcor could not be
used. I agree the Fo(complex)-Fo(apo) gives a much more realistic result
than the MR-solution I suggested.
Tim
--
Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen
GPG Key ID = A46BEE1A
On Thu, 18 Jun 2009, Doug Ohlendorf wrote:
> 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:[log in to unmask]] On Behalf Of Tim
> Gruene
> Sent: Wednesday, June 17, 2009 4:39 PM
> To: [log in to unmask]
> 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
>
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