A single-site mutation (F429H) converts the enzyme CYP 2B4 into a heme oxygenase: a QM/MM study.

The intriguing deactivation of the cytochrome P450 (CYP) 2B4 enzyme induced by mutation of a single residue, Phe429 to His, is explored by quantum mechanical/molecular mechanical calculations of the O–OH bond activation of the (Fe3+OOH)− intermediate. It is found that the F429H mutant of CYP 2B4 undergoes homolytic instead of heterolytic O–OH bond cleavage. Thus, the mutant acquires the following characteristics of a heme oxygenase enzyme: (a) donation by His429 of an additional NH---S H-bond to the cysteine ligand combined with the presence of the substrate retards the heterolytic cleavage and gives rise to homolytic O–OH cleavage, and (b) the Thr302/water cluster orients nascent OH• and ensures efficient meso hydroxylation.