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RE: [ccp4bb]: Re: Xenon at high pressure
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> -----Original Message-----
> From: owner-ccp4bb@dl.ac.uk [mailto:owner-ccp4bb@dl.ac.uk]On Behalf Of
> Rizkallah, PJ (Pierre)
> Sent: Mittwoch, 23. Mai 2001 11:03
> To: 'ernst@UTBC08.CM.UTEXAS.EDU'; CCP4BB@dl.ac.uk
> Subject: RE: [ccp4bb]: Re: Xenon at high pressure
> The Xcell or equivalent commercial products would allow the use
> of pressure
> as far as the cylinder/regulator let through. In this case, the limitation
> is how quickly can the experimentalist take the loop, with the crystal in,
> out of the pressure cell and into the cryostream. People quote a diffusion
> time of a few minutes for Xe through the crystal lattice, i.e. residence
> time in the pressure cell makes no difference beyond 15 minutes. The
> important thing is that in the few seconds it takes to transfer the loop,
> the pressure will have been released. There is no way one can
> tell how much
> Xe is left in the lattice (unless you do some fancy spectroscopy).
Christoph Kratky, one of the Xenon pioneers in this field, once explained to
us that it took about one minute after pressure release before he could see
any difference in the xenon binding to myoglobin (I think he pressurized at
50 bar). He explained the retarded xenon release by a metastable state
(comparable to a bottle of fizzing water that releases only a little bit of
its stored CO2 upon opening, whereas much more CO2 is released if the bottle
is shaken prior to opening). So, if this metastable xenon binding can be
generalized, there shouldn't be much xenon release in the short time that
you need to transfer the crystal to the cry-cooling device.
Good luck,
Dirk.
*****************************************************
Dirk Kostrewa
Paul Scherrer Institut e-mail: dirk.kostrewa@psi.ch
Life Sciences phone: +41-56-310-4722
OSRA/007 fax: +41-56-310-4556
CH-5232 Villigen PSI WWW: http://www.sb.psi.ch
Switzerland
*****************************************************
It
> obviously depends on the lattice in hand. Proteins that bind
> non-polars are
> naturally prediposed to trapping Xe, like the crustacyanin. Those with no
> such binding sites, can still trap Xe at non-obvious places. So one can
> discover where all the hydrophobic patches are on the protein surface. If
> these patches are genuinely absent, then maintaining the pressure at RT
> might be the answer.
>
> As for the suitability of Xe as a derivative, it has a massive 7e
> anomalous
> signal at a wavelength around 1.5 A. The low affinity and natural disorder
> in a poor vdw interaction may reduce the usable signal, but it could still
> be as significant as the 3.7e signal from Se at its correct edge. And with
> synchrotrons, one can use 2.0 A wavelength, where the signal
> becomes 11e. I
> have used Xe with 3 different proteins so far, at wavelengths of 1.488 or
> 2.0 A. Only crustacyanin had an unknown structure, and now it is
> solved. The
> other 2 gave easily interpretable pattersons, and they will be assessed
> properly in the fullness of time. So I claim 100% hit rate, but I'll
> probably fail with the next one. Such is PX!
>
> I hope I have answered all your questions, but please come back
> if there are
> more points to discuss. Cheers, and Happy Pressurising.
>
>
> Pierre Rizkallah
>
> -----Original Message-----
> From: ernst@UTBC08.CM.UTEXAS.EDU [mailto:ernst@UTBC08.CM.UTEXAS.EDU]
> Sent: 22 May 2001 20:26
> To: CCP4BB@dl.ac.uk
> Subject: [ccp4bb]: Re: Xenon at high pressure
>
>
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>
>
> how deep is the ocean, how high is high?
>
> we get to about 400-420 psi with the regulator on our lab cylinder and
> have had one fair derivative out of about 6 trials (3 different proteins).
> pressurized time 10-45 minutes.
>
> gordon webster reported:
>
> Pierre Rizkallah said that he and his colleagues had found Xenon at high
> pressure to be an excellent
> choice, their results for this work on the structure of crustacyanin will
> appear very soon in Acta D.
>
> Steve Ernst
>