Hi Francis,
The asymmetric unit volume is approximately proportional to the number
of atoms in your model, the basis for Vm, with some variation due to
solvent content. In turn the number of unique observations at a given
resolution is proportional to asymmetric unit volume. So twice the
number of atoms means twice the volume and twice the number of
observations. Consequently, the observation/parameter ratio depends
mostly on resolution and at 2 Angstrom you should have a much better
ratio than the one you calculated, unless you have a very low solvent
content, very low data completeness, or, hopefully, you made an error in
your calculation :)
Bart
Francis E Reyes wrote:
All
It seems I have a case where I have 5595 reflections but my protein is
about 102 residues. With a mean atom / residue * 4 parameters for each
atom I get about 7833 parameters. So it seems that I have a
observation : parameter ratio < 1. There is only 1 molecular per asu
so there's no hope in using NCS. Phases to be obtained from a pretty
good MR solution. Does anyone have any
suggestions/protocols/references for refining with obs:parameter < 1 ?
thanks
FR
---------------------------------------------
Francis Reyes M.Sc.
215 UCB
University of Colorado at Boulder
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