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A hierarchy of functionally important relaxations within myoglobin based on solvent effects, mutations and kinetic model
 

Summary: Review
A hierarchy of functionally important relaxations within myoglobin based
on solvent effects, mutations and kinetic model
David Dantskera
, Uri Samunia
, Joel M. Friedmana,*, Noam Agmonb,*
a
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
b
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew University, Jerusalem 91904, Israel
Received 20 February 2005; received in revised form 30 March 2005; accepted 6 April 2005
Available online 25 April 2005
Abstract
Geminate CO rebinding in myoglobin is studied for two viscous solvents, trehalose and sol­gel (bathed in 100% glycerol) at several
temperatures. Mutations in key distal hemepocket residues are used to eliminate or enhance specific relaxation modes. The time-resolved data
are analyzed with a modified Agmon­Hopfield model which is capable of providing excellent fits in cases where a single relaxation mode is
dominant. Using this approach, we determine the relaxation rate constants of specific functionally important modes, obtaining also their
Arrhenius activation energies. We find a hierarchy of distal pocket modes controlling the rebinding kinetics. The ``heme access mode''
(HAM) is responsible for the major slow-down in rebinding. It is a solvent-coupled cooperative mode which restricts ligand return from the
xenon cavities. Bulky side-chains, like those His64 and Trp29 (in the L29W mutant), operate like overdamped pendulums which move over

  

Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem

 

Collections: Chemistry