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overspeeding</title></head><body>
<div>All:</div>
<div><br></div>
<div>Ariel's point is well taken. It reminded me of two other studies
on overspeeding:</div>
<div><br></div>
<div>One very detailed theoretical study from David teller's group in
the 1960's. (cf page 78: D.C. Teller and T.A. Horbett,<font
face="Lucida Grande" size="-4" color="#000000"> "Ultracentrifuge
Studies with Rayleigh Interference Optics. III ...", Annals NY
Academy Sciences pp 66-101.</font>) gives over speeding protocols. It
also warns of the serious dangers of over - overspeeding. In 1976
Dennis Roark published a handy little formula for calculating
overspeed times based on the calculations done by the Teller Lab. The
overspeeding procedures cited can - if properly applied (and properly
is the key word here) - reduce the time to equilibrium to about 1/6 th
the time not using overspeeding. However, if you look at the figure on
page 78, you'll see that the choice of overspeeding time is quite
critical. Use of overspeeding with unknown mixed systems could lead to
undesirable results since each species has a very narrow useable
overspeeding time.</div>
<div><br></div>
<div><font color="#000000"><br></font></div>
<div><font color="#000000"><br></font></div>
<div><font color="#000000">Here is the reference (and abstract) to
Denny's paper.</font></div>
<div><font color="#000000"><br></font></div>
<div><font color="#000000">Roark, D. E. (1976). "Sedimentation
equilibrium techniques: multiple speed analyses and an overspeed
procedure."<u> Biophysical Chemistry</u><b> 5</b>(1-2):
185-96.<br>
<x-tab> </x-tab>The use of a single high-speed sedimentation
equilibrium experiment to analyze mixed associating systems is
inadequate to determine the association mode even if the molecular
weight of one species is known. Simultaneous analysis of the
concentration distributions at three equilibrium speeds greatly
reduces the lack of uniqueness. Linear least-squares multi-speed fits
discriminate between association models in which the molecular weights
are assumed. Experiments at a series of initial concentrations as well
as rotor speeds further increases the discrimination. An overspeed
procedure is proposed. The overspeed time depends only slightly on the
sedimenting species molecular weight, but significantly on the
frictional ratio. A minimal overspeed time may be
estimated.</font><br>
<font color="#000000"></font></div>
<div><br></div>
<div>Walter</div>
<div><br></div>
<div>p.s. Also a must read from David Teller's Lab:<font
face="Lucida Grande" size="-4" color="#000000"> Teller, DC,
Characterization of proteins by sedimentation equilibrium in the
analytical ultracentrifuge. Methods Enzymol.
1973;27:346-441.</font></div>
<div><br></div>
<div><br></div>
<div><br></div>
<div>At 5:58 PM +0200 9/29/04, Ariel Lustig wrote:</div>
<blockquote type="cite" cite><font size="-1">Dear colleauges, lets
come back to reality</font></blockquote>
<blockquote type="cite" cite><font size="-1">At least for
new-comers , but not only for them, the subject of predicting or
better , calculating the time to achieve equilibrium makes no /
or only very little sense , since as I belive that every
one of us use the</font></blockquote>
<blockquote type="cite" cite><font size="-1">"overspeed
procedure" discribed by Hexner, Radford and Beams PNAS
(1961), 47,1848 that reduces time to achieve equilibrium to 50%
or more. If so, I ask myself what means time to equilibrium
? from the time rotor speed is achieved and not yet a
concentration gradient is established, or a steep graient at
both solution column ends? all non -sense ! I agree that for
polydispersed or selfassociating systems</font></blockquote>
<blockquote type="cite" cite><font size="-1">using an
overspeed procedure is difficult (and dangrous especially it
some parts are not reversible), but not less difficult as to calculate
time to equilibrium as you suggested of a non monodispersed
systeme.</font></blockquote>
<blockquote type="cite" cite><font size="-1">In FRACTION N° 1
1967 issued by Beckman Instruments ( may be based on
the same equation</font></blockquote>
<blockquote type="cite" cite><font size="-1">that Walter
Stafford mentioned recently) K.E Van Holde discribed a
formula where the time depends on Diffusion ! and here again to
new-comers. If at all making the<u> exercise</u> to calculate time to
equilibrium.</font></blockquote>
<blockquote type="cite" cite><font size="-1">It is to use
D</font><font size="-2">obs</font><font size="-1"> and not
D</font><font size="-2">20w</font><font size="-1"> that is correected
for Viscosity of water. There may be a huge
difference</font></blockquote>
<blockquote type="cite" cite><font size="-1">between the two
Diffusion values if per example you use sucrose in the
buffer as I do measuring</font></blockquote>
<blockquote type="cite" cite><font size="-1">membrane proteins.
The density has no influence for Diffusion only the
viscosity of the solvent.</font></blockquote>
<blockquote type="cite" cite><font
size="-1">yours....ariel</font></blockquote>
<blockquote type="cite" cite><font
size="-1">ariel.lustig@bluewin.ch</font></blockquote>
<div><br></div>
<div><br></div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div><font face="Times"
color="#0000FF"
>----------------------------------------------------------</font></div
>
<div><font face="Times" color="#0000FF">Walter Stafford</font></div>
<div><font face="Times"
color="#0000FF">mailto:stafford@bbri.org</font></div>
<div><font face="Times" color="#0000FF">direct dial:
617-658-7808</font></div>
<div><font face="Times" color="#0000FF">receptionist:
617-658-7700</font></div>
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