From: Eugene Leitl (Eugene.Leitl@lrz.uni-muenchen.de)
Date: Thu Dec 05 1996 - 11:03:29 MST
On Wed, 4 Dec 1996, Hal Finney wrote:
> From: Lyle Burkhead <LYBRHED@delphi.com>
> > When a protein embedded in a membrane encounters a certain
> > molecule, it reacts -- it suddenly changes its mode of vibration, and
Uh, not "mode of vibration", let's say a change in conformation. Reaction
is a bit much, it is usually reserved to denote encounters resulting in
connectivity change. Here the stuff bonds to a specific spot, the overall
conformation changes. It can be further amplified if this change makes a
protein to become active/nonactive, e.g. release a signal, open an ion
channel, become catalytically active, etc.
> > this change reverberates all over the membrane, causing further changes
All over the membrane? The membrane is a semiflud 2d mosaic, a 2d
liquid crystal. This won't work.
> > in the vibrations of all other proteins embedded in the membrane.
> > As a result of one molecule encountering one protein, pores may
> > open or close all over the membrane, as other proteins react to the
> > change in vibration of the sensor protein.
This is not mediated through the membrane. The closest thing to your
scenario is a transient breakdown of an transmembrane potential
(laboriously maintained by pumping stuff, while burning ATP), which
causes a depolarization, a kind of chain reaction causing ion channel in
the vicinity to open up as well. This defines an excitable medium, able
to propagate signals over spatially large regions of the membrane. (Most
of cell types don't express this). The lipide bilayer has no active part
in this phenomenon.
> > That's how membranes work. At a very low temperature, such
> > pulsations would not exist. The atoms would be nearly motionless.
At low enough temperatures membranes undergo a phase transition. It will
denaturate a large percentile of transmembrane- and membrane-embedded
proteins, which (transiently or permanently) will cease to function.
> > Therefore biological membranes require temperatures in a certain range.
> > Below that range, one would have to use other mechanisms to replace
> > membranes.
Membranes must offer 2d fluidity to function. Biological organisms adapt
to temperature change by changing the chemical composition of the
membrane to remain in the optimal range. The window of adaptability has a
pretty small aperture, however.
> I have never heard of this phenomenon. It would be interesting and
Nor me.
> surprising if this is really how information is transported to the
> various proteins within membranes. I would think the (thermal?) vibrations
By physical means, either chemical messengers, or transmembrane potential
changes.
> of the proteins would be swamped with other thermal noise within the
> membrane environment and be unable to propagate for any distance.
> Is this a real effect, or is this just one of Lyle's games?
Games.
> Hal
ciao,
'gene
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