Ionization dependence of camphor binding and spin conversion of the complex between cytochrome P-450 and camphor. Kinetic and static studies at sub-zero temperatures.
The kinetic rate constants of formation and dissociation of the cytochrome-P-450 - camphor complex (Fe3+-RH) have been obtained by low-temperature (+ 5 degrees C to -20 degrees C) stopped-flow experiments. Simiarly the high-spin/low-spin equilibrium of this complex has been studied as a function of temperature and protonic activity. Both the camphor-binding mechanism and the high-spin/low-spin thermodynamic parameters of Fe3+-RH depend on the protonic activity of the medium in the physiological pH range. The binding rate constants are shown to depend on the ionization of a residue of the protein, probably a histidine. Linear enthalpy-entropy compensation is observed for the camphor binding as well as for the spin-state transition. A camphor-binding-induced change of the electrostatic potential is discussed.
D002151:Calorimetry; D002164:Camphor; D003577:Cytochrome P-450 Enzyme System; D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D011487:Protein Conformation; D011549:Pseudomonas / Q000201:enzymology; D013053:Spectrophotometry; D013816:Thermodynamics
D002164:Camphor; D003577:Cytochrome P-450 Enzyme System