Spin Transition of Camphor‐Bound Cytochrome P‐450

Abstract
Variations of the spin state in camphor‐bound cytochrome P‐450 are interpreted in the light of the polyelectrolyte theory and its implications on the microenvironment of the heme. The ratio of high‐spin to low‐spin iron can serve as a tool to determine the local paH in the microenvironment of a group (pK0,app∼ 5.4) which governs the spin state. The local paH depends on the electrostatic potential created by negatively charged groups (pKa= 5.6), modulated in turn by paH and by the screening effect of ionic strength. A model is given for the proton‐coupled spin state change.