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D.L. Stein: Research on Biophysics - for Physicists
In collaboration with Walter Nadler (University of Juelich,
Germany), I have worked on the problem of ligand migration (e.g., CO
or O2) in globular proteins like myoglobin. There is some beautiful
physics associated with the problem: far from being a random walk of
a point particle on a static lattice, the ligand deforms the protein,
which in turn acts back on the ligand; and the protein is continually
fluctuating while all this is happening. In fact, if the protein were
frozen into its static, average conformation, no ligand diffusion could
occur at all! The fluctuation of the protein at physiological temperatures
(well above its glass transition) opens voids through which the ligand
can travel.
There are many experimental studies of the time-, pressure-, and temperature-dependence
of the diffusion process. Using these to guide our work, we have proposed
and studied a reaction-diffusion model of the process. Our model explains
the observed time-dependence of the ligand recombination following flash
photolysis. More importantly, we proposed a sharp experimental test
to resolve the problem (sometimes referred to as the single-channel
hypothesis) of the dimensionality of the ligand path within the protein.
Our work can also be used to study passive ion-channel fluctuations
in a different class of proteins.
The problem of protein conformational fluctuations has led us to consider
the problem of diffusion on a fluctuating lattice; that is, where the
bonds open and close randomly in time. With David Levermore (Mathematics
Department, University of Maryland), we proposed a renormalization-group
treatment of this problem, whose applications also extend to problems
in other ares: for example, ionic conduction in polymeric solid electrolytes
and protonic diffusion in hydrogen-bonded networks.
For detailed information on our research, see Technical
Publications. Most of my recent publications are downloadable from
this page. (To save both time and paper, the link will take
you to the abstract on the cond-mat archives page. If desired, the full
paper can then be
downloaded from there.)
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Daniel
L. Stein