The heme cofactor and catalytic site

In cytochrome P450cam, the 5th ligand to the heme Fe is a Cysteine S. In substrate-free P450cam, the 6th ligand is a water molecule, the Fe is low spin and its redox state is Fe3+. In camphor-bound P450cam, the 6th ligand water molecule is displaced, the Fe is almost 100% high spin. Reaction takes place on binding of oxygen at the Fe and in the presence of other proteins (putidaredoxin and putidaredoxin reductase) to facilitate the required supply of e- and H+.

Carbon monoxide binds at the Fe and can be used as a probe of the active site environment by spectroscopic techniques. For cytochrome P450cam, 13CO NMR chemical shifts and 12CO infrared stretching frequencies in the presence of various camphor analogues are correlated indicating that steric and electrostatic effects on the CO ligand are influenced by the substrate[6]. However, these cytochrome P450 complexes have this correlation on another line from hemoglobins due to the different proximal ligand.

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Wade et al. (1996) Fundamentals of Enzyme-Ligand Interactions in Cytochrome P450cam
POPE5 Conference Proceedings
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