Hi Sudheer,

As other researchers, I guess, will address hemoglobin iron properties, I would reply on what is known about heme iron of P450s (CYPs). CYP enzymes catalyze a variety of oxidation and some reduction reactions, a general chemical mechanism can be used to rationalize most of the oxidations and involves a perfenyl intermediate (FeO3+) and odd-electron chemistry, i.e. abstraction of a hydrogen atom or electron followed by oxygen rebound and sometimes rearrangement. To the matter of your question, this general mechanism can explain what major substrate groups involved in the binding to CYP heme iron in the monooxygenase-type reactions, such as carbon hydroxylation, heteroatom oxygenation and dealkylation, epoxidation, and desaturation. Let me present here just a single example - benzene hydroxylation, which is a fundamental process in chemical catalysis. In nature, this reaction is catalyzed by the CYP via oxygen transfer in a still debated mechanism of considerable complexity. Hybrid density functional calculations were used to elucidate the mechanisms by which benzene is converted to phenol, benzene oxide, and ketone, by the active species of the enzyme, the high-valent iron-oxo porphyrin species. The effects of the protein polarity and hydrogen-bonding donation to the active species were mimicked. It was verified that the reaction does not proceed either by hydrogen abstraction or by initial electron transfer. The dominant reaction channel is electrophilic and proceeds via the cationic sigma-complex,  (2)3, that involves an internal ion pair made from a cationic benzene moiety and an anionic iron porphyrin.

Best wishes,

Ilya