Open AccessThe Low‐Spin ⇌ High‐Spin Transition of Camphor‐Bound Cytochrome P ‐450
Author(s) -
LANGE Reinhard,
BONFILS Claude,
DEBEY Pascale
Publication year - 1977
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1977.tb11847.x
Subject(s) - chemistry , ionic strength , spin (aerodynamics) , spin transition , aqueous solution , spin states , enthalpy , camphor , solvent , ionic bonding , equilibrium constant , thermodynamics , inorganic chemistry , ion , crystallography , organic chemistry , physics
The spin state of camphor‐bound cytochrome P ‐450 is shown to depend largely on medium and temperature in aqueous as well as in mixed organic buffer. At sub‐zero temperatures a variation of p a H , ionic strength or camphor concentration modifies the spin equilibrium from nearly pure high‐spin form to nearly pure low‐spin form. Since the apparent p K a of transition is a linear function of log I , the spin state seems to be controlled by the electrostatic potential in the heme proximity. K + is found to have a specific effect on the spin state. The change of enthalpy, Δ H values, of the spin transition depends on the same parameters as the equilibrium constant, in the organic cosolvent as well as in aqueous buffer. As the cosolvent effect is reflected by higher Δ H values, and KCI and pH tend to lower Δ H , the cosolvent effect can easily be compensated. Therefore kinetic studies of the spin conversion might well be undertaken at sub‐zero temperature in this solvent.