Dear all
Thanks for all your suggestions. PO4 is from my Ligand PI3P, but I cannot see the electron density of the PI3P tail, and the binding site is exactly there. While my crystal buffer salt is 50mM (NH4)2SO4, so I am afraid the SO4 occupied the PO4 position.BTW, I can see the other SO4 electron density in the other places, but is small than this one, and the diffraction resolution is 1.6A.
Best Regards
Shijun
-----Original Messages-----
From:"Roger Rowlett" <[log in to unmask]>
Sent Time:2019-02-17 00:47:55 (Sunday)
To: [log in to unmask]
Cc:
Subject: Re: [ccp4bb] SO4 or PO4
Two things to look at that could provide a clue:
Examine the anomalous map for some density over the central atom. Sulfur will often, but not always have significant anomalous density depending on the wavelength and quality of data set.
Phosphate is normally HPO4= or H2PO4-. Look for phosphate donor to acceptor hydrogen bonding contacts. Sulfate rarely has donor to acceptor hydrogen bonding contacts, as it is SO4= at any reasonable pH.
Roger Rowlett
Dear all
I have got a crystal grown at the condition both have ion of SO4 and PO4, and the diffraction resolution is very well, but the problem is coming: how to tell which is which just from electron density? I think they are exactly same. Thanks a lot !!!
Beat Regards
Shijun
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