The ability of peroxidases and laccases enzymes to treat organic pollutants is reviewed. Enzymatic methods generally have low energy requirements, are easy to control, can operate over a wide range of conditions and have a minimal environmental impact. Peroxidases and laccases have broad substrate specificities and can catalyze the oxidation of a wide range of toxic organic compounds. The results show that an enzymatic oxidation can diminish the toxicity of some polycyclic aromatic hydrocarbons (PAHs), phenols, organophosphorus pesticides and azo dyes in laboratory and some field conditions. Due to the hydrophobicity and low aqueous solubility of these substrates, reactions are usually performed in the presence of organic solvents. However, it was detected that organic solvents can provoke enzyme denaturation, unfavorable substrate partition, inhibition or stabilization of enzyme–substrate complexes, depending on the enzyme, substrate and organic solvent used. Strategies to overcome these problems are proposed. Additionally, the low stability of heme-containing peroxidases to hydrogen peroxide, the low reaction rates of laccases, the mediators toxicity, the limited availability and high costs of these enzymes are other limitations detected for commercial applications. Due to field reaction conditions are more complex than laboratory conditions efforts have to be made to achieve the cheap overproduction of these biocatalysts in heterologous hosts and also their modification by chemical means or protein engineering to obtain more robust and active enzymes.

Potential use of oxidative enzymes for the detoxification of organic pollutants

Active site structure and catalytic mechanisms of human peroxidases.

Collagen IV comprises the predominant protein network of basement membranes, a specialized extracellular matrix, which underlie epithelia and endothelia. These networks assemble through oligomerization and covalent crosslinking to endow mechanical strength and shape cell behavior through interactions with cell-surface receptors. A recently discovered sulfilimine (S=N) bond between a methionine sulfur and hydroxylysine nitrogen reinforces the collagen IV network. We demonstrate that peroxidasin, an enzyme found in basement membranes, catalyzes formation of the sulfilimine bond. Drosophila peroxidasin mutants have disorganized collagen IV networks and torn visceral muscle basement membranes, pointing to a critical role for the enzyme in tissue biogenesis. Peroxidasin generates hypohalous acids as reaction intermediates, suggesting a paradoxically anabolic role for these usually destructive oxidants. This work highlights sulfilimine bond formation as what is to our knowledge the first known physiologic function for peroxidasin, a role for hypohalous oxidants in tissue biogenesis, and a possible role for peroxidasin in inflammatory diseases.

Peroxidasin forms sulfilimine chemical bonds using hypohalous acids in tissue genesis

H2O2 is the usual oxidizing substrate of horseradish peroxidase C (HRP-C). In the absence in the reaction medium of a one-electron donor substrate, H2O2 is able to act as both oxidizing and reducing substrate. However, under these conditions the enzyme also undergoes a progressive loss of activity. There are several pathways that maintain the activity of the enzyme by recovering the ferric form, one of which is the decomposition of H2O2 to molecular oxygen in a similar way to the action of catalase. This production of oxygen has been kinetically characterized with a Clark-type electrode coupled to an oxygraph. HRP-C exhibits a weak catalase-like activity, the initial reaction rate of which is hyperbolically dependent on the H2O2 concentration, with values for K(2) (affinity of the first intermediate, compound I, for H2O2) and k(3) (apparent rate constant controlling catalase activity) of 4.0 +/- 0.6 mM and 1.78 +/- 0.12 s(-1) respectively. Oxygen production by HRP-C is favoured at pH values greater than approx. 6.5; under similar conditions HRP-C is also much less sensitive to inactivation during incubations with H2O2. We therefore suggest that this pathway is a major protective mechanism of HRP-C against such inactivation.

Catalase-like activity of horseradish peroxidase: relationship to enzyme inactivation by H2O2.

Iodine transfers in the coastal marine environment: the key role of brown algae and of their vanadium-dependent haloperoxidases.

Non-stoichiometric (excessive) consumption of hydrogen peroxide (H2O2), which was observed in various lactoperoxidase-catalysed reactions, was tested in the lactoperoxidase/H2O2/iodide system. In preliminary experiments the suitability of the system was tested with special regard to the triiodide (I−3) absorption and the I2/I−3 equilibrium. Triiodide equilibrium concentrations evaluated theoretically and experimentally were compared after adding a known amount of iodine (I2) to solutions containing variable I− concentrations. A close fit of the two methods was only obtained if experiments were carried out in pure aqueous or 0.001 M H2SO4 medium. The presence of various anions, e.g. OH− and Cl−, led to a measurable decrease in I−3 and I2 equilibrium concentrations. These ions are able to displace competitively I− in forming association products with I+ and I2. When I+ and I2 were generated enzymatically by lactoperoxidase and hydrogen peroxide, additional interactions with H2O2 were observed. Depending on the enzyme and iodide concentrations, variable amounts of H2O2 disappeared non-productively. Due to its ambivalent redox reactivity, part of the H2O2 is not reduced to H2O in the enzyme-catalysed generation of iodine, but undergoes oxidation to O2 by an oxidized iodine compound. This suggests a pseudocatalatic side reaction which can competitively interfere with the I2 I−3 generation or (and) the iodination reaction.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1984.tb08158.x

Pseudo-catalytic degradation of hydrogen peroxide in the lactoperoxidase/H2O2/iodide system.

In the presence of iodide (I-, 10 mM) and hydrogen peroxide in a large excess (H2O2, 0.1-10 mM) catalytic amounts of lactoperoxidase (2 nM) are very rapidly irreversibly inactivated without forming compound III (cpd III). In contrast, in the absence of I- cpd III is formed and inactivation proceeds very slowly. Increasing the enzyme concentration up to the micromolar range significantly accelerates the rate of inactivation. The present data reveal that irreversible inactivation of the enzyme involves cleavage of the prosthetic group and liberation of heme iron. The rate of enzyme destruction is well correlated with the production of molecular oxygen (O2), which originates from the oxidation of excess H2O2. Since H2O2 and O2 per se do not affect the heme moiety of the peroxidase, we suggest that the damaging species may be a primary intermediate of the H2O2 oxidation, such as oxygen in its excited singlet state (1 delta gO2), superoxide radicals (O-.2), or consequently formed hydroxyl radicals (OH.).

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1986.tb09798.x

The role of compound III in reversible and irreversible inactivation of lactoperoxidase

Non-enzymatic (I2-mediated) and lactoperoxidase-catalyzed iodination of tyrosine are inhibited by excess iodide (I-) and/or hydrogen peroxide (H2O2). This phenomenon is a consequence of the concentration-dependent dual role of I- and H2O2 in the iodinating system. I- and H2O2, in addition to their function as primary substrates of peroxidase, may act as alternative 'iodine acceptors' and therefore compete with tyrosine for the active iodinating agent, irrespective of whether this compound is an enzyme-associated iodinium cation (E X I delta +) or an equivalent oxidized iodine species (IOH, IC1, I2). The competitive reaction pathways resulting from excess I- and/or H2O2 in the iodination system are I2/I-3 generation and/or pseudo-catalatic degradation of H2O2, respectively. Our results also demonstrate that I2 (and alternative medium-dependent oxidized iodine species such as IOH and IC1) generated in the iodination system may play an important role as iodinating agent(s). They serve as a substitute for the enzyme-bound iodinium species (E X I delta +), if the prevailing I- concentration favours this pathway. The proposed mechanism of the various antagonistic and interactive reaction pathways is summarized in a scheme.

Mechanism of enzymatic and non-enzymatic tyrosine iodination Inhibition by excess hydrogen peroxide and/or iodide

Iodination of tyrosyl residues and the coupling reaction to produce the thyroid hormones are catalyzed by one single enzyme, the thyroid peroxidase. In addition to the two substrates, tyrosine and I−, the presence of H2O2 is required. Though the overall pathway for the two reactions has been known for a long time, the molecular mechanism, and especially the regulatory functions of I− and H2O2, are still a matter of debate. In this report we present evidence that H2O2 and I− are not merely essential substrates but, in addition, they may be involved in the regulation of enzyme activity.

Irreversible Inactivation of Lactoperoxidase by Excess Hydrogen Peroxide Involving Cleavage of the Catalytic Heme Moiety

In 1939, Lefébure & Chenevière described the Cretaceous fossil species Kittonia hannae Lefébure & Chenevière (1939: 23 pl. 1, fig. 3, see Sims & Williams 2022: fig. 8). The specimen figured was from the Moreno Shale deposit, California, USA, supplied by Dallas Hanna (1887–1970): “Moreno shale, Moreno Gulch in the Panoche Hills, Fresno County, California” […] “Sec. 6, T. 15 S., R. 12 E., M.D.B. & M., Fresno County, California” (Hanna 1934: 352, see also Hanna in Long et al. 1946: 91, Hanna 1927, Rampi 1940, Goudkoff 1945). Other specimens of Kittonia hannae were from another Moreno Shale exposure, “Sec. 24, T. 14, S., R. 11 E., Fresno County, California” (Hanna in Long et al. 1946: 93, Brigger & Hanna 1965: 4). A detailed discussion of the Moreno deposit can be found in Hanna (1927: 10), Long et al. (1946), Nikolaev et al. (2001) and Davies et al. (2012), and a review of the genus Kittonia was undertaken by Brigger & Hanna (1965).

Martin Huwiler

Papers

Pseudo-catalytic degradation of hydrogen peroxide in the lactoperoxidase/H2O2/iodide system.

The role of compound III in reversible and irreversible inactivation of lactoperoxidase

Mechanism of enzymatic and non-enzymatic tyrosine iodination Inhibition by excess hydrogen peroxide and/or iodide

Irreversible Inactivation of Lactoperoxidase by Excess Hydrogen Peroxide Involving Cleavage of the Catalytic Heme Moiety

A note on the specimens of Kittonia hannae ‘hannai’ (Bacillariophyta) figured in Long et al. (1946)