Re: [ccp4bb]: Cys modification

[Manfred Buehner <buehner@biozentrum.uni-wuerzburg.de>]

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On Mon, 17 Apr 2000, Jeff Taylor wrote:

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> 
> I've also been wondering about extra density that I see near the two
> cysteines in the model I'm working on.  The data are up to 1.7A and were
> collected at 100K.  Replacing the SH with SO3 does not fit well, in
> either case.  The extra density is to one side of the sulfur and I
> currently have it modeled as a magnesium ion.  Water doesn't fit well

Magnesium is not probable since it makes a lousy sulfide, How about
zink? Zink is a common impurity, it is a minor component of some
lab glasses (e.g. the old Schott G 20) from where traces are dis-
solved by alkaline buffers. In the alkaline pH range zink forms a
decently stable sulfide. EDTA should prevent this, but if none is
used zink is omnipresent in trace concentrations.

Manfred
----------------------------------------------------------
 Dr. Manfred Buehner             Phone:  +49-931-888-4100
 Physiologische Chemie           FAX:    +49-931-888-4150
 Theodor-Boveri-Institut fuer Biowissenschaften
 Biozentrum der Universitaet Wuerzburg
 Am Hubland,  D-97074 WUERZBURG,  Germany
 Email:  buehner@biozentrum.uni-wuerzburg.de
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