Active intermediates in heme monooxygenase reactions as revealed by cryoreduction/annealing, EPR/ENDOR studies

This review describes the use of cryoreduction/annealing EPR/ENDOR techniques for determining the active oxidizing species in reactions catalyzed by heme monooxygenases. The three candidate heme states are: ferric peroxo, ferric hydroperoxo and compound I intermediates. The enzymes discussed include cytochromes P450, nitric oxide synthase and heme oxygenase.

Research highlights
► EPR/ENDOR spectroscopy of radiolytically cryoreduced oxyheme monooxygenases has identified the active oxidizing species in: (1) cytochrome P450 reactions; (2) the two stages by which NOS generates NO; (3) meso-heme hydroxylation by heme oxygenases.
► It has also demonstrated the influence of substrate in modulating monooxygenase activity.