Heme Enzyme Structure and Function

The review focuses on those enzymes that catalyze oxidation reactions and those for which crystal structures are available. There are two broad classes of heme enzyme oxidants: oxygenases that use O2 to oxidize, oxygenate, substrates and peroxidases that use 2O2 to oxidize. The review demonstrates that out of the oxidants molecular oxygen is the most unusual, as O2 is not a reactive molecule despite the oxidation of nearly all biological molecules by O2 being a thermodynamically favorable process. The reason is that there is a large kinetic barrier to these reactions owing to O2 being a paramagnetic molecule so that the reaction between a majority of biological molecules that have paired spins is a spin forbidden process.