Stein: Research on Biophysics
Physical analysis of biological problems, and - in the
opposite direction - biological inspiration of new physical and mathematical
problems, go back a very long way. However, the previous few decades
have seen an unprecedented growth of biological physics.
My work covers only a tiny part of the large spectrum of activities
in the field. My research in other areas has naturally led me to pursue
some of the many problems in biology where random processes play an
important role. Of these, one of the more intriguing (to me, anyway)
is the process by which a molecule of oxygen finds its way from the
outside of a hemoglobin molecule (in a red blood cell) to the iron-containing
heme group deep in the interior, to which the oxygen molecule binds.
Although the hemoglobin molecule (a protein) is much larger than an
oxygen molecule, it is tightly packed in most places. So, if the protein
remained perfectly rigid, the oxygen could never enter very far (and
we'd all be dead).
It turns out that getting the oxygen molecule to the deep interior of
the protein, where it binds to the heme group, depends on the rapid
fluctuations of the protein. At physiological temperatures, hemoglobin
and many other proteins continually flit in and out of different spatial
conformations. In the present example, this creates (momentarily, and
at sort of random locations) large enough holes for the oxygen molecule
to diffuse through.