Note on the Reduction of Ferryl Heme by Hydrogen Peroxide

I was meaning to change this diagram to show the product that would be expected (the superoxide anion):

The point is that there's thought to be an unknown mechanism by which that superoxide can donate another electron to iron(IV), in ferryl heme in some peroxidase enzymes, to produce molecular oxygen and water, which I've drawn as one of the coordinating ligands. I should draw the reduction mechanism in the case of the hydrogen abstraction from an unsaturated fatty acid [RH ---> R(e-) + H(e-) (a hydrogen atom and an alkyl radical, R(e-), that can go on to form a lipid hydroperoxide and then a lipid alkoxyl radical, etc.)]. That's the overall reaction in the reduction of ferryl heme by hydrogen peroxide--a hydrogen abstraction (shown below). It makes more sense in view of that article by Traylor et al. (1993), cited in the previous posting. The reaction is very similar to an epoxidation, and Traylor et al. (1993) used different hemes to form epoxides in high yields. But ferryl heme doesn't normally form epoxides in vivo. They had to use special conditions. Incidentally, a hydrogen abstraction isn't the same as a hydride transfer: