Effects of monovalent cations on cytochrome P‐450 camphor evidence for preferential binding of potassium

Abstract Binding of monovalent cations of increasing ionic radius to ferric cytochrome P-450 cam was measured. Potassium has the highest affinity for the cation binding site observed in the X-ray crystallographic structure with K d cat = 12 mM, compared with the smaller cation lithium, ( K d cat = 37 mM) and the larger cation cesium ( K d cat = 20 mM). Coupling between cation binding and camphor binding is established by the observation of a linear relationship between the corresponding binding free energies. Potassium binding favours a conformational change of tyrosine 96 which increases the affinity of the protein for camphor and fully dehydrates the active site.