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

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Abstract
Binding of monovalent cations of increasing ionic radius to ferric cytochrome P‐450cam 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.