Article

Conformational substates of horse heart cytochrome c exhibit different thermal unfolding of the heme cavity.

Department of Chemistry, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, USA.
The Journal of Physical Chemistry B (impact factor: 3.7). 09/2007; 111(32):9603-7. DOI:10.1021/jp069022j
Source: PubMed

ABSTRACT The charge transfer (CT) band at 695 nm in the spectrum of ferri-cytochrome c is highly asymmetric, indicating conformational heterogeneity due to the coexistence of different conformational substates. We have measured the respective band profile of horse heart ferri-cytochrome c as a function of temperature between 283 K (10 degrees C) and 333 K (60 degrees C) and found that the well-known decrease of the absorptivity is wavenumber-dependent and exhibits a biphasic behavior. This indicates that the underlying conformational substates differ in their thermodynamic stability with respect to the structural changes associated with the disappearance of the 695 nm band, which eventually (at high temperatures) involves the replacement of M80 by a nearby lysine residue. Our data further indicates that the thermal unfolding process involves two structurally different intermediate states.

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Keywords

10 degrees C
 
60 degrees C
 
biphasic behavior
 
charge transfer
 
conformational heterogeneity
 
different conformational substates
 
ferri-cytochrome c
 
horse heart ferri-cytochrome c
 
lysine residue
 
respective band profile
 
structural changes
 
structurally different intermediate states
 
thermodynamic stability
 
underlying conformational substates
 
well-known decrease