Iron sulfur proteins tend to absorb less (although not zero) in the visible
when reduced. We see this with succinate dehydrogenase when we reduce with
dithionite to see the heme spectrum- the difference extinction coefficient
at the beta "peak" is actually negative because the baseline absorbance
due to three different Fe-S centers is bleached. (Acta Cryst. D61,
380 Fig 2)
Published spectra for soluble Rieske protein fragments also show bleaching.
Yuri Pompeu wrote:
Actually with haeme, and or flavin containing enzymes it is known for the
cofactor to undergo reduction.
There is a recent JACS paper that explores these changes as a function of X-ray
exposure.
(2012) J.Am.Chem.Soc. 134: 2823-2834
Excellent work done in part at Allen Orville's X6A
As far as quality of your data goes, unless your crystal is suffering from
radiation damage (they all do!) from those free electrons/radicals
then your data should not be affected by the bleaching.
HTH.
Yuri
RHYS GRINTER wrote:
Hi All,
I was collecting some data at home on a crystal from a protein containing a
ferredoxin domain. This crystal was originally red-brown in colour, but after
16h of data collection, a large portion of it appears not be colourless. The
crystal still seems to diffract fine (beyond 2A).
I assume this it due in some way to the radiation exposure but was wondering
out curiosity whether someone had experienced this before and had a specific
explanation for it. And if this will effect the integrity of the data.
Cheers
Rhys Grinter
PhD Candidate
University of Glasgow
