• Prosthetic group features
• Peroxidase reaction
• Haem peroxidases in PROMISE
• Haem peroxidases in motif databases
• References

Haem type	Haem iron coordination	Axial iron ligand(s)	Formal iron oxidation/spin states
Haem b	Pentacoordinate / Hexacoordinate	NHis; (H2O or OH¯)	FeII (S=2); FeIII (S=5/2)
	Hexacoordinate	NHis; H2O, H2O2 or O2	FeII (S=0); FeIII (S=1/2)
	Hexacoordinate	NHis; O (O·)	FeIV (S=1)

Peroxidases are haem­containing enzymes that use hydrogen peroxide (H₂O₂) as the electron acceptor to catalyse a number of oxidative reactions. Most haem peroxidases follow the reaction scheme [1, 2]:

In this mechanism, the enzyme reacts with one equivalent of H₂O₂ to give compound I, a porphyrin ­cation radical containing Fe^IV. This is a two­electron oxidation/reduction reaction where H₂O₂ is reduced to water and the enzyme is oxidised. One oxidising equivalent resides on iron, giving the oxyferryl (Fe^IV=O) intermediate. Compound I then oxidises an organic substrate to give a substrate radical (·AH). Compound I undergoes a second one­electron oxidation reaction yielding compound II, which contains an oxyferryl centre coordinated to a normal (dianionic) porphyrin ligand. Finally, compound II, is reduced back to the native ferric state with concomitant one­electron substrate oxidation. The overall charge on the resting state and compound I is +1, while compound II is neutral (cf. catalase and chloroperoxidase).

Peroxidases are found in bacteria, fungi, plants and animals. On the basis of sequence similarity, haem peroxidases can be categorised into two superfamilies: fungal, plant and bacterial peroxidases form one superfamily [3] and animal enzymes form another [4].

Haem peroxidases in PROMISE

PROMISE ID	Description
ANPEROXIDASE	Animal haem peroxidases (myeloperoxidase, eosinophil peroxidase, lactoperoxidase, thyroid peroxidase, prostaglandin H synthase, peroxidasin)
FPBPEROXIDASE	Fungal, plant and bacterial haem peroxidases (yeast cytochrome c peroxidase, ascorbate peroxidase, bacterial catalase­peroxidases, lignin peroxidase, manganese peroxidase, secretory plant peroxidases).

References

1. Kaim, W. and Schwederski, B. (1991) Bioinorganic Chemistry: Inorganic Elements in the Chemistry of Life. Wiley, Chichester.
2. Dawson, J.H. (1988) Probing structure­function relations in heme­containing oxygenases and peroxidases. Science 240, 433-439.
3. Welinder, K.G. (1992) Superfamily of plant, fungal and bacterial peroxidases. Curr. Opin. Struct. Biol. 2, 388-393.
4. Kimura, S. and Ikeda­Saito, M. (1988) Human myeloperoxidase and thyroid peroxidase, two enzymes with separate and distinct physiological functions, are evolutionarily related members of the same gene family. Proteins 3, 113-120.