RE: [ccp4bb]: SUMMARY: Selenomethionine oxidation during RP-HPLC

["Bernhard Rupp" <br@llnl.gov>]

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> -----Original Message-----
> From: owner-ccp4bb@dl.ac.uk [mailto:owner-ccp4bb@dl.ac.uk]On Behalf Of
> Axel Innis
> Sent: Friday, May 11, 2001 3:21 AM
> To: ccp4bb@dl.ac.uk
> Subject: [ccp4bb]: SUMMARY: Selenomethionine oxidation during RP-HPLC
> - Why not do the structure with oxidised SeMet protein. Oxidised selenium
> gives a stronger MAD signal than reduced selenium. The problem is when you
> get mixed oxidation states, because then you don't get any absorption peak
> at all.

Pardon me but do not get that. The Se has a absorption edge, no matter what.
The stronger 'oxidized' edge is probably an electronic effect at the XANES
creating
an additional component seen as a white line feature (the peak above the
edge jump level). A different chemical environment shifts the edges (up
energy when oxidized, few eV) and may lead to a superposition and thus
broadening of the edge. The no signal theory I do not understand?

I also do not quite understand what exact species the 'oxidized Selenium'
or what oxidized Se-Met actually is. Does anyone have some insight into
that?

Thx, BR