Heme-thiolate peroxidases

CPO from the sooty mold L. fumago is the model enzyme for the heme-thiolate family, and has been described as one of the most versatile of all heme enzymes [81]. Recently, a second type of heme-thiolate peroxidase has been discovered first in A. aegerita [82] and latter in cultures and genomes of other basidiomycetes (see Sect. 3.2.2). The new enzyme exhibits a wider biotechnological interest than 

CPO due to its ability to transfer oxygen not only to typical CPO substrates but also to different aromatics, such as naphthalene or benzene [45, 46]. Therefore, the name aromatic peroxygenase has been suggested for the A. aegerita heme-thiolate peroxidase [83, 84]. 

Although CPO was first describe in 1966 [85] it was not until 1995 that its crystal structure was solved [27]. The crystal structure of the novel heme-thiolate aromatic -peroxygenase from A. aegerita has not been yet published, therefore, the CPO molecular structure is described herein as representative for the heme-thiolate peroxidases. 

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Our laboratory is also studying the directed evolution of a new type of potentially ligninolytic peroxidase classified as unspecific peroxygenase, UPO (EG 1.11.2.1). UPO was initially defined as a heme-thiolate peroxidase, exhibiting both per-oxidative and peroxygenative activities toward aromatic compounds (aromatic peroxygenase, also referred to as APO [26, 75]). However, more recent studies have described the monooxygenase activity of UPO toward ahphatic compounds (UPO,... 

Gutierrez, A., Babot, E.D., Ullrich, R., Hofrichter, M., Martmez, A.T., and del Rfo, J.C. (2011) Regioselective oxygenation of fatty acids, fatty alcohols and other aliphatic compounds by a basid-iomycete heme-thiolate peroxidase. Arch. Biochem. Biophys., 514, 33-43. 

A review has been written on the topic of synthetic active-site analogues of heme-thiolate proteins. As well as cytochrome P450, models for chloro-peroxidase are dicussed. Alkanethiolate-coordinated iron porphyrins and their dioxygen adducts have been synthesized and characterized as P450 models. ... 

Cytochrome P-450, which is the most extensively studied of the monooxygenase proteins, has a heme-iron active center with an axial thiol ligand (a cysteine residue). However, most chemical model investigations use simple iron(III) porphyrins without thiolate ligands. As a result, model mechanisms for cytochrome P-450 invoke a reactive intermediate that is formulated to be equivalent to Compound I of horseradish peroxidase, (por+-)Fe =0, with a high-potential porphyrin cation radical. Such a species would be reduced by thiolate, and therefore is an unreasonable formulation for the reactive center of cytochrome P-450. 

P450 chloroperoxidase contains a thiolate group of a cysteine side chain as the fifth iron ligand. Chloroperoxidase forms compounds 1 and 11, as do other peroxidases. A chloride ion may combine with compound 1 to form a complex of hypochlorite with the Fe(lll) heme. 

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