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e.d. emanating from cysteines


I was considering posting this message to bionet.xtallography but out of the
the 10 messages posted since 24th August, I noticed that 5 are selling sex
manuals, "the software THEY DON'T WANT YOU TO HAVE!!!", sewing machines,
mushrooms, dodgy business startups in undefined "imports", etc. Are any
crystallographers actually reading the list or are they waving the white
flag in the face of such a barrage of drivel?

Anyway, I have some extended electron density in several maps from
differently soaked crystals of the same protein. It begins exactly halfway
between two cysteines which are located with their side chains facing each
other, 4.4 apart, and extends 7-8 out into the solution, bifurcating
slightly at the end. The crystals were grown and soaked in DTT, in buffers
also including MgCl2 and Tris. The protein has seen mostly Tris buffer
during the purification. Has anyone seen this kind of modification before?
Does DTT ever bind covalently to the protein? With apologies to anyone
reading their E-mail over a 28.8K modem, I've included a GIF file of the
e.d. as an attachment. The map is at 2.4 resolution.

Thanks for sharing any experiences you may have had (but send them in a
plain brown envelope, please...)


Dr. Derek Logan
Dept. of Biochemistry   tel: +46 8 162454
Stockholm University    fax: +46 8 153679
S-106 91 Stockholm           +1 503 210-1066