Dioxygen reactivity of meso-hydroxylated hemes: intermediates in heme degradation process catalyzed by heme oxygenase

Heme oxygenase (HO) is the only enzyme in mammals known to catalyse the physiological degradation of unwanted heme into biliverdin, Fe ion and CO. The process involves introduction of the hydroxyl group at one of its meso-positions as the first fundamental step of the heme cleavage process. It was also found that meso-amino heme undergoes similar ring-cleavage process while reacting with dioxygen in presence of pyridine as an axial ligand. The present paper briefly reviews the reactions of model meso-hydroxylated heme and its analogues with dioxygen, and their relevance in the heme degradation process.