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Rick Venable rvenable at deimos.cber.nih.gov
Thu Jan 26 21:41:18 EST 1995

On Thu, 26 Jan 1995 22:53:19 GMT Mohan Srinivasan pontificated:
> 	Can proteins fold in a different way in the absence of
> gravity ? I believe that their density changes (compacts) when
> spun in ultracentrifuges at high rpm's (high G). So, the reverse 
> (low G) should be also true. Gravity is one of the forces apart
> from the nuclear forces. Does folding depend only on nuclear
> forces ?  I am not sure though. Was any study made in this direction 
> during space experiments ? Could anyone throw some light ?

I'd say that there is little or no difference.  First, the difference
between 0 G and 1 G is very small, compared to the high G force in a
modern ultracentrifuge.  Second, perhaps many astronauts would be dead if
the change from 1 G to 0 G seriously altered protein folding.  Third, most
theoretical chemistry programs (molecular dynamics, quantum calculations,
etc.) ignore gravity completely.  Not that the absence is proof, but many
leading scientists studying protein folding from a theoretical approach do
not consider gravity.  After all, the mass of a protein is infintesimal
compared to the mass of the Earth, and it exists in a buoyant medium.

Folding does not depend on nuclear forces, but electrostatic forces (charge
attraction and repulsion) and the mostly attractive London dispersion, or van
der Waals, forces.  The charge interactions can be fairly long range, easily
2-5 times the zero point as van der Waals forces; the latter forces are close
to zero for atom interactions further than 10 Angstroms apart.

Finally, I'm sure there have been 0 G protein crystallization experiments on
the space shuttle, as well as a fair number of biochemistry and biological
experiments.  Perhaps they've even made blood density measurements.  NASA
is very foward about providing access to the results of their work, both as
publications and on-line thru gopher and www servers.

Rick Venable                  =====\     |=|    "Eschew Obfuscation"
FDA/CBER Biophysics Lab       |____/     |=|
Bethesda, MD  U.S.A.          |   \  /   |=|  / Not an official statement \
rvenable at deimos.cber.nih.gov       \/    |=|  \  or position of the FDA.  /

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