Spectroscopic characterization of the acid–alkaline transition of a thermophilic cytochrome P450

The spectroscopic properties of thermophilic cytochrome P450 from the thermoacidophilic crenarchaeon Sulfolobus tokodaii strain 7 (P450st) were investigated in acidic and basic solutions. The resting form of ferric-P450st in weakly-acidic and neutral solutions contained a thiolate/H2O coordinated low-spin heme. Below pH 1.5, P450st underwent cleavage of the Fe–S bond and was converted into apo-P450st. Above pH 8, the acid–alkaline transition due to the deprotonation of the water ligand was observed. The produced thiolate/OH−-coordinated ferric-P450st was stable at room temperature. The pKa value of 8.7 for the transition reflects the protonation properties of the distal side of the heme.

► A thermostable cytochrome P450 exhibits two transitions between pH 1 and 11. ► The heme of P450st dissociates below pH 1.5 by cleavage of the Fe–S bond. ► The deprotonation of the water ligand takes place with the pKa value of 8.7.