Bromoperoxidases from Penicillus capitatus, Penicillus lamourouxii and Rhipocephalus phoenix

Halogenating Enzymes for Active Agent Synthesis: First Steps Are Done and Many Have to Follow

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.

Biogenic Iodine and Iodine-Containing Metabolites

This review is intended as a comprehensive survey of iodinated metabolites possessing carbon–iodine covalent bond, which have been obtained from living organisms. Generally thought to be minor components produced by many different organisms these interesting compounds now number more than 110. Many from isolated and identified iodine-containing metabolites showed high biological activities. Recent research, especially in the marine area, indicates this number will increase in the future. Sources of iodinated metabolites include microorganisms, algae, marine invertebrates, and some animals. Their origin and possible biological significance have also been discussed.

Environmental Control of Vanadium Haloperoxidases and Halocarbon Emissions in Macroalgae

Vanadium-dependent haloperoxidases (V-HPO), able to catalyze the reaction of halide ions (Cl^-, Br^-, I^-) with hydrogen peroxide, have a great influence on the production of halocarbons, which in turn are involved in atmospheric ozone destruction and global warming. The production of these haloperoxidases in macroalgae is influenced by changes in the surrounding environment. The first reported vanadium bromoperoxidase was discovered 40 years ago in the brown alga Ascophyllum nodosum. Since that discovery, more studies have been conducted on the structure and mechanism of the enzyme, mainly focused on three types of V-HPO, the chloro- and bromoperoxidases and, more recently, the iodoperoxidase. Since aspects of environmental regulation of haloperoxidases are less well known, the present paper will focus on reviewing the factors which influence the production of these enzymes in macroalgae, particularly their interactions with reactive oxygen species (ROS).

Marine Vanadium-Dependent Haloperoxidases, Their Isolation, Characterization, and Application

Vanadium-dependent haloperoxidases in seaweeds, cyanobacteria, fungi, and possibly phytoplankton play an important role in the release of halogenated volatile compounds in the environment. These halocarbons have effects on atmospheric chemistry since they cause ozone depletion. In this chapter, a survey is given of the different sources of these enzymes, some of their properties, the various methods to isolate them, and the bottlenecks in purification. The assays to detect and quantify haloperoxidase activity are described as well as their kinetic properties. Several practical tips and pitfalls are given which have not yet been published explicitly. Recent developments in research on structure and function of these enzymes are reviewed. Finally, the application of vanadium-dependent haloperoxidases in the biosynthesis of brominated and other compounds is discussed.

Exploring the links between natural products and bacterial assemblages in the sponge Aplysina aerophoba

The sponge Aplysina aerophoba produces a large diversity of brominated alkaloids (BAs) and hosts a complex microbial assemblage. Although BAs are located within sponge cells, the enzymes that bind halogen elements to organic compounds have been exclusively described in algae, fungi, and bacteria. Bacterial communities within A. aerophoba could therefore be involved in the biosynthesis of these compounds. This study investigates whether changes in both the concentration of BAs and the bacterial assemblages are correlated in A. aerophoba. To do so, we quantified major natural products using high-performance liquid chromatography and analyzed bacterial assemblages using denaturing gradient gel electrophoresis on the 16S rRNA gene. We identified multiple associations between bacteria and natural products, including a strong relationship between a Chloroflexi phylotype and aplysinamisin-1 and between an unidentified bacterium and aerophobin-2 and isofistularin-3. Our results suggest that these bacteria could either be involved in the production of BAs or be directly affected by them. To our knowledge, this is one of the first reports that find a significant correlation between natural products and bacterial populations in any benthic organism. Further investigating these associations will shed light on the organization and functioning of host-endobiont systems such as Aplysina aerophoba.

Heme-thiolate haloperoxidases: versatile biocatalysts with biotechnological and environmental significance

Heme-thiolate haloperoxidases are undoubtedly the most versatile biocatalysts of the hemeprotein family and share catalytic properties with at least three further classes of heme-containing oxidoreductases, namely, classic plant and fungal peroxidases, cytochrome P450 monooxygenases, and catalases. For a long time, only one enzyme of this type--the chloroperoxidase (CPO) of the ascomycete Caldariomyces fumago--has been known. The enzyme is commercially available as a fine chemical and catalyzes the unspecific chlorination, bromination, and iodation (but no fluorination) of a variety of electrophilic organic substrates via hypohalous acid as actual halogenating agent. In the absence of halide, CPO resembles cytochrome P450s and epoxidizes and hydroxylates activated substrates such as organic sulfides and olefins; aromatic rings, however, are not susceptible to CPO-catalyzed oxygen-transfer. Recently, a second fungal haloperoxidase of the heme-thiolate type has been discovered in the agaric mushroom Agrocybe aegerita. The UV-Vis adsorption spectrum of the isolated enzyme shows little similarity to that of CPO but is almost identical to a resting-state P450. The Agrocybe aegerita peroxidase (AaP) has strong brominating as well as weak chlorinating and iodating activities, and catalyzes both benzylic and aromatic hydroxylations (e.g., of toluene and naphthalene). AaP and related fungal peroxidases could become promising biocatalysts in biotechnological applications because they seemingly fill the gap between CPO and P450 enzymes and act as "self-sufficient" peroxygenases. From the environmental point of view, the existence of a halogenating mushroom enzyme is interesting because it could be linked to the multitude of halogenated compounds known from these organisms.

Biosynthesis of halogenated metabolites by bacteria

Halogenated metabolites, originally thought to be infrequent in nature, are actually nothing unusual at all, and are produced by many different organisms, including bacteria. Whereas marine bacteria usually produce brominated compounds, terrestrial bacteria preferentially synthesize chlorometabolites, but fluoro- and iodometabolites can also be found. Haloperoxidases, enzymes capable of catalyzing the formation of carbon halogen bonds in the presence of hydrogen peroxide and halide ions (Cl-, Br- and I-) have been isolated and characterized from different bacteria. These enzymes turned out to be very unspecific and are obviously not the type of halogenating enzymes responsible for the formation of halometabolites in bacteria. A yet-unknown type of halogenating enzyme having both substrate and regio-specificity must be involved in the biosynthesis of halogenated compounds.

Bacterial haloperoxidases and their role in secondary metabolism

Bacteria produce a large number of different halogenated secondary metabolites. Haloperoxidases are believed to be the enzymes responsible for the halogenation reaction. Two classes of haloperoxidases, heme and nonheme, were isolated from different bacteria and their role in the biosynthesis of halogenated secondary metabolites was investigated. Two genes of bacterial haloperoxidases were cloned and can now be used to produce large quantities of the enzymes.

On the repair of thymidine bromohydrins, damaged nucleosides: a possible new model for the damage and repair of nucleic acids

Bromohydrins, which were damaged products of thymidines (2, 3, and 4), were repaired with sunlight or heat via a radical mechanism to regenerate the thymidines. A hypothesis for the biological significance of thymidine in DNA is presented.

Detection of a new chloroperoxidase in Pseudomonas pyrrocinia

A new chloroperoxidase could be detected in Pseudomonas pyrrocinia ATCC 15,958, a bacterium that produces the antifungal antibiotic pyrrolnitrin. This enzyme was separated from a ferriprotoporphyrin IX containing bromoperoxidase which was also produced by this bacterium. The enzyme is capable of catalyzing the chorination of indole to 7-chloroindole. This procaryotic chloroperoxidase requires the presence of H2O2 and can also brominate monochlorodimedone, but cannot catalyze its chlorination. This enzyme is the first chloroperoxidase described from procaryotic sources.

Purification of bromoperoxidase from Corallina pilulifera

Bromoperoxidase was purified from the crude extract of Corallina pilulifera (Corallinaeae, Rhodophyta) and found to be homogeneous upon disc gel electrophoresis by precipitation of ammonium sulfate and sequential column chromatographies of DEAE-Sepharose CL-6B, Sepharose 6B and Cellulofine GC-700m. The purified enzyme did not exhibit optical absorption spectra of a hemoprotein. Therefore, bromoperoxidase of C. pilulifera was completely distinguishable from other haloperoxidases which have heme-irons at the catalytic sites.

Purification of bromoperoxidase from Pseudomonas aureofaciens

A Bromoperoxidase has been isolated and purified from Pseudomonas aureofaciens ATCC 15926 mutant strain ACN. The purified enzyme was homogeneous as determined by polyacrylamide gel electrophoresis and ultracentrifugation. This bromoperoxidase can utilize bromide ions in the presence of hydrogen peroxide and a halogen acceptor for the catalytic formation of carbon-halogen bonds. The homogeneous enzyme also has peroxidase and catalase activity. Based on the results from gel filtration and ultracentrifugation, the molecular weight of this procaryotic bromoperoxidase is 155,000 to 158,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows a single band having the mobility of a 77,000-molecular-weight species. We thus conclude that this bromoperoxidase exists in solution as a dimeric species. The heme prosthetic group of bromoperoxidase is ferriprotoporphyrin IX. The spectral properties of the native and reduced enzyme are reported. This bromoperoxidase is the first halogenating enzyme purified from procaryotic sources.

Predictable spatial escapes from herbivory: how do these affect the evolution of herbivore resistance in tropical marine communities?

Between-habitat differences in macrophyte consumption by herbivorous fishes were examined on three Caribbean and two Indian Ocean coral reefs. Transplanted sections of seagrasses were used as a bioassay to compare removal rates in reef-slope, reef-flat, sand-plain, and lagoon habitats. Herbivore susceptibility of fifty-two species of seaweeds from these habitats was also measured in the field. Seagrass consumption on shallow reef slopes was always significantly greater than on shallow reef flats, deep sand plains, or sandy lagoons. Reef-slope seaweeds were consistently resistant to herbivory while reef-flat seaweeds were consistently very susceptible to herbivory. This pattern supports the hypothesis that defenses against herbivores are costly in terms of fitness and are selected against in habitats with predictably low rates of herbivory.Sand-plain and lagoon seaweeds showed a mixed response when placed in habitats with high herbivore pressure; most fleshy red seaweeds were eaten rapidly, most fleshy green seaweeds were eaten at intermediate rates, and most calcified green seaweeds were avoided or eaten at very low rates. Differences in susceptibility between red and green seaweeds from sand-plain or lagoon habitats may result from differential competitive pressures experienced by these seaweed groups or from the differential probability of being encountered by herbivores. The susceptibility of a species to removal by herbivorous fishes was relatively consistent between reefs. Preferences of the sea urchin Diadema antillarum were also similar to those of the fish guilds.Unique secondary metabolites were characteristic of almost all of the most herbivore resistant seaweeds. However, some of the herbivore susceptible species also contain chemicals that have been proposed as defensive compounds. Genera such as Sargassum, Turbinaria, Thalassia, Halodule, and Thalassodendron, which produce polyphenolics or phenolic acids, were consumed at high to intermediate rates, suggesting that these compounds are not effective deterrents for some herbivorous fishes. Additionally, potential for the production of the compounds caulerpin, caulerpicin and caulerpenyne in various species of Caulerpa did not assure low susceptibility to herbivory.Heavily calcified seaweeds were very resistant to herbivory, but all of these species also produce toxic secondary metabolites which makes it difficult to distinguish between the effects of morphological and chemical defenses. Predictions of susceptibility to herbivory based on algal toughness and external morphology were of limited value in explaining differing resistances to herbivory.

Detection of a bromoperoxidase in Streptomyces phaeochromogenes

A bromoperoxidase could be detected after fractionation in the chloramphenicol producing actinomycete, Streptomyces phaeochromogenes. This enzyme is capable of catalyzing the bromination of the antifungal antibiotic pyrrolnitrin [3-chloro-4-(2-nitro-3-chlorophenyl)pyrrole] in the 2-position of the pyrrole ring. The enzyme had a pH optimum of 5.0. This procaryotic bromoperoxidase requires the presence of H2O2 and can also brominate monochlorodimedone, but cannot catalyze chlorination. This enzyme is the first haloperoxidase described from procaryotic sources.

The action of chloride peroxidase on 4-chloroaniline. N-oxidation and ring halogenation

Chloride peroxidase catalyses both the ring halogenation and N-oxidation reactions of 4-chloroaniline by H2O2 and either KCl or KBr. In the absence of any halide salt only the N-oxidation reaction was observed, with the resulting conversion of 4-chloroaniline into 4-chloronitrosobenzene. The N-oxidation reaction proceeded even more rapidly in the presence of Cl- or Br-, in spite of the fact that ring halogenation was also a rapid reaction. The enhancement of N-oxidation was highly dependent on the pH of the media and displayed an optimum in the region of pH 3.5-4.0. No rate enhancement was observed above pH 5.5. KF partially inhibited the rate of N-oxidation in a pH-dependent manner. On the basis of calculated catalytic-centre activity the N-oxidation reaction was the major reaction at pH 3.5 or higher, whereas the ring-halogenation reaction became the major reaction below pH 3.5. In the presence of high concentrations of 4-chloroaniline relative to H2O2 the reaction intermediate, 4-chlorophenylhydroxylamine, was detected for the first time in a chloride peroxidase-catalysed reaction with this arylamine substrate. These findings were interpreted on the basis of current knowledge concerning the mechanism of action of chloride peroxidase.