Mixed metal sites and B-factors

M.Hough mhh at mscsv1.dl.ac.uk
Fri Jan 21 08:24:45 EST 2000



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Dr Mike Hough			Phone: Work: 01925 603658
Molecular Biophysics Group	       
Daresbury Laboratory
Warrington			       mhh at dl.ac.uk
WA4 4AD
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Dear all

I have a series of enzyme structures in which a metal ion (Cu) occupies a series of positions intermediate between those expected for the Cu(I) and Cu(II) forms
of the system. The position between the end points is ~0.6 Angstrom and the intermediates lie mid-way between those points. The most likely explanation is that photoreduction is occuring and I am observing a mixture of Cu(II) and Cu(I) sites.

My question is:

If I model a single,, full occupancy Cu atom and this refines in REFMAC to an intermediate position between the two forms, would I expect to see any of the following.

1) An increase in the isotropic B-factor for the metal
2) Increased anisotropy for the metal
3) Elongation of the density.

I see a certain degree of 3) but not 1) or 2)o

 am using REFMAC, with good quality data to 1.65 Angstrom

 Is it likely that I am seeing photoreduction here, or something else
 
 Thanks,
 
 Mike
 
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