Isolation and characterization of a thermostable intracellular enzyme with peroxidase activity from Bacillus sphaericus

During a screening for bacteria producing enzymes with peroxidase activity, a Bacillus sphaericus strain was isolated. This strain was found to contain an intracellular enzyme with peroxidase activity. The native enzyme had a molecular mass of above 300 kDa and precipitated at a salt concentration higher than 0.1 M. Proteolytic digestion with trypsin reduced the molecular mass of the active enzyme to 13 kDa (dimer) or 26 kDa (tetramer) and increased its solubility, allowing purification to homogeneity. Spectroscopic investigations showed the enzyme to be a hemoenzyme containing heme c as the covalently bound prosthetic group. The enzyme was stable up to 90 degrees C and at alkaline conditions up to pH 11, with a pH optimum at pH 8.5. It could be visualized by activity staining after SDS-PAGE and showed activity with a number of typical substrates for peroxidases, e.g., 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) diammonium salt, guaiacol and 2,4-dichlorophenol; however the enzyme had no catalase and cytochrome c peroxidase activity.

Microbial biosynthesis of halometabolites

Halometabolites are compounds that are commonly found in nature and they are produced by many different organisms. Whereas bromometabolites can mainly be found in the marine environment, chlorometabolites are predominately produced by terrestrial organisms; iodo- and fluorocompounds are only produced infrequently. The halogen atoms are incorporated into organic compounds by enzyme-catalyzed reactions with halide ions as the halogen source. For over 40 years haloperoxidases were thought to be responsible for the incorporation of halogen atoms into organic molecules. However, haloperoxidases lack substrate specificity and regioselectivity, and the connection of haloperoxidases with the in vivo formation of halometabolites has never been demonstrated. Recently, molecular genetic investigations showed that, at least in bacteria, a different class of halogenases is involved in halometabolite formation. These halogenases were found to require FADH2, which can be produced from FAD and NADH by unspecific flavin reductases. In addition to FADH2, oxygen and halide ions (chloride and bromide) are necessary for the halogenation reaction. The FADH2-dependent halogenases show substrate specificity and regioselectivity, and their genes have been detected in many halometabolite-producing bacteria, suggesting that this type of halogenating enzymes constitutes the major source for halometabolite formation in bacteria and possibly also in other organisms.

Specific enzymatic chlorination of tryptophan and tryptophan derivatives

In the search for an alternative to chemical halogenation reactions using the free halogens, a novel type of halogenating enzymes was detected. In contrast to haloperoxidases, these NADH-dependent halogenases are specific. Tryptophan halogenase which catalyses the regioselective chlorination of tryptophan to 7-chlorotryptophan can also chlorinate tryptamine, tryptophol, indole-3-acetonitrile, and 3-methylindole. However, indole-3-acetonitrile is not chlorinated in the 7-position, but in positions two and three of the indole ring. Chlorination in the 3-position is obviously stereospecific. In addition to tryptophan and indole derivatives, aminophenylpyrrole is also accepted as a substrate for regioselective chlorination. Since the new NADH-dependent halogenases have a fairly broad substrate specificity and catalyse regioselective chlorination reactions they could be a good alternative to chemical halogenation.

Enzymatic halogenation catalyzed via a catalytic triad and by oxidoreductases

During the search for haloperoxidases in bacteria we detected a type of enzymes that catalyzed the peroxide-dependent halogenation of organic substrates. However, in contrast to already known haloperoxidases, these enzymes do not contain a prosthetic group or metal ions nor any other cofactor. Biochemical and molecular genetic studies revealed that they contain a catalytic triad consisting of a serine, a histidine, and an aspartate. The reaction they catalyze is actually the perhydrolysis of an acetic acid serine ester leading to the formation of peracetic acid. As a strong oxidizing agent the enzymatically formed peracetic acid can oxidize halide ions, resulting in the formation of hypohalous acid which then acts as the actual halogenating agent. Since hypohalous acid is also formed by the heme- and vanadium-containing haloperoxidases, enzymatic halogenation catalyzed by haloperoxidases and perhydrolases in general lacks substrate specificity and regioselectivity. However, detailed studies on the biosynthesis of several halometabolites led to the detection of a novel type of halogenases. These enzymes consist of a two-component system and require NADH and FAD for activity. Whereas the gene for one of the components is part of the biosynthetic cluster of the halometabolite, the second component is an enzyme which is also present in bacteria from which no halometabolites have ever been isolated, like Escherichia coli. In contrast to haloperoxidases and perhydrolases the newly detected NADH/FAD-dependent halogenases are substrate-specific and regioselective and might provide ideal tools for specific halogenation reactions.

Structural investigation of the cofactor-free chloroperoxidases

The structures of cofactor-free haloperoxidases from Streptomyces aureofaciens, Streptomyces lividans, and Pseudomonas fluorescens have been determined at resolutions between 1.9 A and 1.5 A. The structures of two enzymes complexed with benzoate or propionate identify the binding site for the organic acids which are required for the haloperoxidase activity. Based on these complexes and on the structure of an inactive variant, a reaction mechanism is proposed for the halogenation reaction with peroxoacid and hypohalous acid as reaction intermediates. Comparison of the structures suggests that a specific halide binding site is absent in the enzymes but that hydrophobic organic compounds may fit into the active site pocket for halogenation at preferential sites.

Functions encoded by pyrrolnitrin biosynthetic genes from Pseudomonas fluorescens

Pyrrolnitrin is a secondary metabolite derived from tryptophan and has strong antifungal activity. Recently we described four genes, prnABCD, from Pseudomonas fluorescens that encode the biosynthesis of pyrrolnitrin. In the work presented here, we describe the function of each prn gene product. The four genes encode proteins identical in size and serology to proteins present in wild-type Pseudomonas fluorescens, but absent from a mutant from which the entire prn gene region had been deleted. The prnA gene product catalyzes the chlorination of L-tryptophan to form 7-chloro-L-tryptophan. The prnB gene product catalyzes a ring rearrangement and decarboxylation to convert 7-chloro-L-tryptophan to monodechloroaminopyrrolnitrin. The prnC gene product chlorinates monodechloroaminopyrrolnitrin at the 3 position to form aminopyrrolnitrin. The prnD gene product catalyzes the oxidation of the amino group of aminopyrrolnitrin to a nitro group to form pyrrolnitrin. The organization of the prn genes in the operon is identical to the order of the reactions in the biosynthetic pathway.

Thiocarbamate herbicide-inducible nonheme haloperoxidase of Rhodococcus erythropolis NI86/21

During biodegradation of thiocarbamate herbicides by Rhodococcus erythropolis NI86/21, a protein with an M(r) of 30,000 is induced (I. Nagy, G. Schoofs, F. Compernolle, P. Proost, J. Vanderleyden, and R.De Mot, J. Bacteriol. 177:676-687, 1995). Based on N-terminal sequence data for the protein purified by two-dimensional electrophoresis, the corresponding structural gene, thcF, was cloned and sequenced. The deduced protein sequence of ThcF is homologous to those of nonheme haloperoxidases. A particularly high level of sequence identity (72.6%) was observed for the chloroperoxidase from Pseudomonas pyrrocinia. A polyclonal antibody against the latter enzyme cross-reacted with ThcF either produced by the original Rhodococcus cells or overexpressed heterologously in Escherichia coli. In both thiocarbamate-grown Rhodococcus cells and E. coli cells expressing thcF, the haloperoxidase activity of ThcF was demonstrated. The thiocarbamate-inducible R. erythropolis ThcF protein represents the first (nonheme) haloperoxidase to be identified in a nocardioform actinomycete.

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.

The non-haem chloroperoxidase from Pseudomonas fluorescens and its relationship to pyrrolnitrin biosynthesis

The non-haem chloroperoxidase gene (cpoF) from the pyrrolnitrin producer Pseudomonas fluorescens BL914 was cloned using an oligonucleotide derived from part of the N-terminal amino acid sequence of chloroperoxidase (CPO-P) from Pseudomonas pyrrocina as a probe. Based on the overexpression of cpoF in Escherichia coli and the stability of CPO-F against higher temperatures and proteases, the enzyme was purified to homogeneity. Partial characterization of the enzyme showed that it belongs to the class of bacterial non-haem CPOs. To investigate the role of CPO-F in pyrrolnitrin biosynthesis, the cpoF gene was inactivated by insertion of a kanamycin cassette. Exchange of the chromosomal cpoF gene against the disrupted copy had no influence on pyrrolnitrin production demonstrating that CPO-F was not involved in pyrrolnitrin biosynthesis.

Purification and properties of a non-haem chloroperoxidase from Serratia marcescens

A non-haem chloroperoxidase was isolated from the enteric bacterium Serratia marcescens. The enzyme was purified to homogeneity by heat treatment, ammonium sulfate precipitation, ion exchange chromatography, gel filtration and dye-ligand affinity chromatography. Native chloroperoxidase has a molecular mass of 58 kDa and consists of two identical subunits of 29 kDa. Whereas chloroperoxidase catalyses only the bromination of monochlorodimedone, indole is chlorinated by this enzyme. Chloroperoxidase also catalyses the oxidation of amino to nitro groups. The enzyme is thermostable and does not lose any activity when incubated at 65 degrees C for 2 h. Comparison of the first 15 amino-terminal amino acids showed a sequence identity of 80% to the chloroperoxidases from Streptomyces lividans and Pseudomonas pyrrocinia. However, no precipitation band was obtained in the Ouchterlony agar diffusion assay with antibodies raised against the chloroperoxidases from Pseudomonas pyrrocinia and Streptomyces aureofaciens Tü24.

The metal-ion-free oxidoreductase from Streptomyces aureofaciens has an alpha/beta hydrolase fold

The crystal structure of the bromoperoxidase A2 from Streptomyces aureofaciens (ATCC 10762) has been determined by isomorphous replacement and refined to 2.05 A resolution with an R-value of 18.4%. The enzyme catalyzes the bromination of organic compounds in the presence of bromide and peroxide. The structure confirms the absence of cofactors such as metal ions or haem groups and shows the general topology of the alpha/beta hydrolase fold. The active centre is at the end of a deep pocket and includes a catalytic triad of Ser 98, Asp 228 and His 257. The active centre is connected by a narrow tunnel to a second pocket on the enzyme surface.

Chloroperoxidase from Streptomyces lividans: isolation and characterization of the enzyme and the corresponding gene

For the first time, a halogenating enzyme which is not known to produce halogenated metabolites has been isolated from a bacterial strain. The gene encoding the nonheme chloroperoxidase (CPO-L) from Streptomyces lividans TK64 was cloned, and its gene product was characterized. S. lividans TK64 produced only very small amounts of the enzyme. After cloning of the gene into Streptomyces aureofaciens Tü24-88, the enzyme was overexpressed up to 3,000-fold. Based on the overexpression, a simple purification procedure using acid precipitation and hydrophobic interaction chromatography was developed. Thus, 54 mg of homogeneous CPO-L could be obtained from 27 g (wet weight) of mycelium. The native enzyme has a molecular weight of 64,000 and consists of two identical subunits. The enzyme does not exhibit an absorption peak in the Soret region of the optical spectrum. X-ray fluorescence spectroscopy revealed that the enzyme does not contain any metal ions in equimolar amounts. CPO-L showed cross-reaction with antibodies raised against the nonheme chloroperoxidase from Pseudomonas pyrrocinia but not with antibodies raised against CPO-T from S. aureofaciens Tü24. CPO-L exhibits substrate specificity only for chlorination, not for bromination. Therefore, monochlorodimedone is only brominated by CPO-L, whereas indole is brominated and chlorinated. The functional chloroperoxidase gene was located on a 1.9-kb SalI DNA fragment. DNA sequence analysis revealed an open reading frame encoding a predicted polypeptide of 276 amino acids. The overall identity of the amino acid sequence to that of chloroperoxidase from P. pyrrocinia was 71%, whereas that to bromoperoxidase BPO-A2 from S. aureofaciens ATCC 10762 was only 42%.

Cloning of a second non-haem bromoperoxidase gene from Streptomyces aureofaciens ATCC 10762: sequence analysis, expression in Streptomyces lividans and enzyme purification

The gene for BPO-A1, one of two non-haem bromoperoxidases in the tetracycline and 7-chlorotetracycline producer Streptomyces aureofaciens ATCC 10762, was cloned in the positive selection vector pIJ699 and expressed in Streptomyces lividans TK64. The cloned bromoperoxidase was over-produced up to 2800-fold by the S. lividans TK64 transformant. By taking advantage of the over-production of BPO-A1 and the heat stability of the enzyme, a new and simple purification procedure was developed. Subcloning into the vector pIJ487 and screening of recombinants by a newly developed histochemical assay located the bpoA1 gene on a 2.1 kb BamHI-HindIII fragment. The nucleotide sequence of the 2.1 kb fragment was determined; the bpoA1 gene was identified within the sequence on the basis of the biased codon usage of Streptomyces genes and the presence of a nucleotide sequence encoding the N-terminal amino acid sequence obtained from the purified BPO-A1. Comparison of the deduced primary structure of BPO-A1 with those deduced for the non-haem chloroperoxidase CPO-P from Pseudomonas pyrrocinia and the bromoperoxidase BPO-A2 from S. aureofaciens ATCC 10762 gave amino acid sequence identities of 49% and 40%, respectively.

The catechol 2,3-dioxygenase gene of Rhodococcus rhodochrous CTM: nucleotide sequence, comparison with isofunctional dioxygenases and evidence for an active-site histidine

In cell-free extracts of Escherichia coli clones harbouring the 3.5 kb Bg/II fragment of plasmid pTC1 from Rhodococcus rhodochrous CTM a catechol 2,3-dioxygenase (C23O) accepting both 3-methylcatechol and 2,3-dihydroxybiphenyl as substrates could be detected. The plasmid-encoded gene for C23O of R. rhodochrous CTM and its flanking regions were sequenced. In front of the gene a sequence resembling an E. coli promoter was identified, which led to constitutive expression of the cloned gene in E. coli TG1. The derived amino acid sequence of the C23O was compared to that of nine other enzymes, which all catalyse the extradiol cleavage of an aromatic ring. These nine sequences were from different Pseudomonas strains, in contrast to the sequence described here, from a Gram-positive bacterium. The role of four strongly conserved histidines was examined by chemical modification of the histidyl residues of the native enzyme by diethylpyrocarbonate. For that purpose the C23O was purified to homogeneity from E. coli harbouring pSC1701. However, the enzyme lost its activity during the purification. Activity could partially be restored by treatment with Fe2+ and reducing agents.

Chloroperoxidase-encoding gene from Pseudomonas pyrrocinia: sequence, expression in heterologous hosts, and purification of the enzyme

The nucleotide sequence of a 1.5-kb fragment of Pseudomonas pyrrocinia DNA containing the chloroperoxidase(CPO)-encoding gene (cpo) and its flanking regions was determined. The cpo codes for a protein of 278 amino acids (aa). The matuŕe enzyme contains no N-terminal methionine, so that the CPO monomer consists of 277 aa with a calculated M(r) of 30,304. Expression studies showed that the cpo from P. pyrrocinia is functionally expressed in Escherichia coli and Streptomyces lividans. Based on the overproduction of the CPO in E. coli, a novel and simple purification procedure was developed allowing the isolation of about 800-fold more CPO per gram of cells than was originally isolated from P. pyrrocinia. Comparison with the aa sequence of the bromoperoxidase BPO-A2 from S. aureofaciens ATCC10762 revealed an identity of 38%.

Molecular cloning and sequencing of a non-haem bromoperoxidase gene from Streptomyces aureofaciens ATCC 10762

A bromoperoxidase gene (bpoT), recently cloned from Streptomyces aureofaciens Tü24, was used as a probe in Southern blot hybridization of total DNA from S. aureofaciens ATCC 10762. A single SstI fragment of 5.4 kb was detected, which was cloned via an enriched gene library into Escherichia coli. The functional bromoperoxidase gene was located on a 2.1 kb BamHI-HindIII fragment by subcloning into S. lividans TK64, using the multicopy plasmid pIJ486. The enzyme was overproduced in S. lividans TK64 (up to 30,000 times compared to S. aureofaciens ATCC 10762) and showed the same electrophoretic and immunological properties as the bromoperoxidase BPO-A2 purified from S. aureofaciens ATCC 10762. DNA sequence analysis revealed an open reading frame encoding a predicted polypeptide with the same M(r) and N-terminal amino acid sequence as the purified subunit of BPO-A2.

Purification, characterization and comparison of two non-haem bromoperoxidases from Streptomyces aureofaciens ATCC 10762

Two non-haem bromoperoxidases (BPO 1 and BPO 2) were purified from the 7-chlorotetracycline-producing strain Streptomyces aureofaciens ATCC 10762. Both enzymes showed azide-insensitive brominating activity, and bromide-dependent peroxidase activity. BPO 1 was a dimer (Mr 65,000) with subunits of identical size (Mr 31,000). The pI was estimated to be 4.5. The enzyme did not cross-react with antibodies raised against the non-haem bromoperoxidase (Mr 90,000) from S. aureofaciens Tü24, a strain that also produces 7-chlorotetracycline. The Mr of BPO 2 was estimated to be 90,000. The enzyme had three identical subunits (Mr 31,000), and its isoelectric point was 3.5, identical with that of the bromoperoxidase from S. aureofaciens Tü24. Moreover, BPO 2 was immunologically identical with the bromoperoxidase from S. aureofaciens Tü24, although both it and BPO 1 could be distinguished electrophoretically from the latter bromoperoxidase.

Crystallization and preliminary X-ray data of bromoperoxidase from Streptomyces aureofaciens ATCC 10762

Bromoperoxidase from Streptomyces aureofaciens ATCC 10762, a non-haem haloperoxidase, has been crystallized using the hanging drop method. Preliminary X-ray diffraction studies show that the crystals belong to the cubic space group P2(1)3 with a = 123.4 A. The asymmetric unit contains a dimer of Mr = 60,200. The crystals diffract to at least 2.3 A resolution and are suitable for crystallographic structure analysis.

Purification, properties and immunological detection of a bromoperoxidase-catalase from Streptomyces venezuelae and from a chloramphenicol-nonproducing mutant

A new bromoperoxidase-catalase was purified from the chloramphenicol-producing actinomycete Streptomyces venezuelae ISP 5230. The homogeneous enzyme showed brominating activity, catalase activity and a very low peroxidase activity. The spectral properties and pH dependence of the catalase activity showed similarities to conventional catalases. In contrast to other haem-bromoperoxidases, the bromoperoxidase-catalase was stable when treated with an ethanol/chloroform mixture. Gel filtration gave an estimated Mr of 127,000-136,000. SDS-PAGE showed a single band corresponding in mobility to a species with an Mr of 61,000. The pI was estimated to be 4.5. The bromoperoxidase-catalase was not present in active form in a mutant of S. venezuelae ISP 5230, blocked in the chlorination step of chloramphenicol biosynthesis. However, an inactive species of the enzyme was detected in crude extracts of the mutant by using antibodies. From these results it is concluded that this bromoperoxidase participates in the chlorination step during chloramphenicol biosynthesis.

Molecular cloning and high-level expression of a bromoperoxidase gene from Streptomyces aureofaciens Tü24

A bromoperoxidase gene was cloned from Streptomyces aureofaciens Tü24 into Streptomyces lividans TK64 by using the promoter-probe vector pIJ486. Subcloning of DNA from the original, unstable clone allowed the gene to be localized to a 1.7-kilobase (kb) fragment of DNA. Southern blotting showed that the cloned 1.7-kb insert hybridized to a 4.3-kb fragment in an SstI digest of S. aureofaciens Tü24 total DNA. The 1.7-kb insert was shown to code for a protein with the electrophoretic properties of the subunits of the nonheme bromoperoxidase isolated from S. aureofaciens Tü24. The protein produced by S. lividans TK64 transformed with pHM621, which contained an 8.0-kb insert, was shown to be identical to the S. aureofaciens Tü24 bromoperoxidase in terms of its electrophoretic mobility on denaturing and nondenaturing polyacrylamide gels and its NH2-terminal amino acid sequence. The bromoperoxidase was overproduced (up to 180 times) by S. lividans TK64 containing pHM621. Based on the heat stability of the S. aureofaciens Tü24 bromoperoxidase, a new and simple purification procedure with very high yields was developed.

Cloning and high-level expression of a chloroperoxidase gene from Pseudomonas pyrrocinia in Escherichia coli

A chloroperoxidase gene from Pseudomonas pyrrocinia was cloned into Escherichia coli using the cosmid vector pJB8. The gene coding for the chloroperoxidase could be localized to a 1.5 kb fragment of DNA which was subcloned into the high-copy-number plasmid pUC18. In one subclone increased halogenating activity could be found which was 570-fold greater than in P. pyrrocinia. The halogenating enzyme was identified as the chloroperoxidase by SDS-polyacrylamide gel electrophoresis.

Purification and characterization of a novel bacterial non-heme chloroperoxidase from Pseudomonas pyrrocinia

The first bacterial chloroperoxidase that is capable of catalyzing the chlorination of indole to 7-chloroindole was detected in Pseudomonas pyrrocinia ATCC 15958, a bacterium that produces the antifungal antibiotic pyrrolnitrin (Wiesner, W., van Pée, K.H., and Lingens, F. (1986) FEBS Lett. 209, 321-324). Here we describe the purification and characterization of this bacterial non-heme chloroperoxidase. The enzyme was purified by DEAE-cellulose chromatography at different pH values, molecular sieve chromatography, and Bio-Gel HTP hydroxylapatite. After the last purification step, chloroperoxidase was homogeneous by polyacrylamide gel electrophoresis and ultracentrifugation. Based on gel filtration and ultracentrifugation results, the molecular weight of the enzyme was 64,000 +/- 3,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a single band with the mobility of a 32,000 molecular weight species. Therefore, in solution at neutral pH, this chloroperoxidase is a dimer. The enzyme did not exhibit any absorbance in the visible region of the spectrum. The isoelectric point was 4.1. Chloroperoxidase was specific for I-, Br-, and Cl- and was not inhibited by azide, but was inhibited by cyanide and F-. This procaryotic chloroperoxidase catalyzed the bromination of monochlorodimedone but not its chlorination and has no peroxidase or catalase activity. The pH optimum of the enzyme was between 4.0 and 4.5, and the enzyme was stable between pH 3.5 and 8.5 and showed no loss of activity when incubated at 60 degrees C for 2 h. Chloroperoxidase also chlorinated 4-(2-amino-3-chlorophenyl) pyrrole to yield aminopyrrolnitrin, the immediate precursor of pyrrolnitrin. This suggests very strongly that chloroperoxidase is involved in the biosynthesis of the antibiotic pyrrolnitrin.

Purification and properties of bromoperoxidase from Pseudomonas pyrrocinia

A bromoperoxidase was purified and partially characterized from Pseudomonas pyrrocinia ATCC 15958, a bacterium that produces the antifungal antibiotic pyrrolnitrin. The purified enzyme preparation was homogeneous as determined by polyacrylamide gel electrophoresis and ultracentrifugation. The molecular mass of the enzyme was estimated to be 154 kDa +/- 3 kDa as determined by gel filtration and ultracentrifugation. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed a single band with the mobility of a 76-kDa species. Therefore, in solution at neutral pH, bromoperoxidase exists as a dimeric species. The isoelectric point was 5.0. The prosthetic group of this procaryotic bromoperoxidase was ferriprotoporphyrin IX. The spectral properties of the native and reduced enzyme are reported. The purified enzyme showed brominating as well as peroxidase and catalase activity.

Purification and molecular and catalytic properties of bromoperoxidase from Streptomyces phaeochromogenes

A bromoperoxidase has been isolated and purified from the chloramphenicol-producing actinomycete Streptomyces phaeochromogenes. The purified enzyme was homogeneous as determined by polyacrylamide gel electrophoresis. The prosthetic group of the bromoperoxidase was ferriprotoporphyrin IX. Based on gel filtration results the molecular weight of the enzyme was 147 000 +/- 3000. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a single band having the mobility of a 72 500 molecular weight species. Therefore, in solution at neutral pH, the bromoperoxidase behaved as a dimer. The isoelectric point was 4.0. The spectral properties of the native and reduced enzyme are reported. The homogeneous enzyme also had peroxidase and catalase activity.

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.

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 biosynthesis of brominated pyrrolnitrin derivatives by Pseudomonas aureofaciens

The mutant strain ACN of Pseudomonas aureofaciens ATCC 15926 produces several bromo derivatives of pyrrolnitrin. Five brominated amino- and three brominated nitrophenyl pyrrole compounds could be isolated, and their structures were established by 1H NMR, UV and mass spectroscopy. The isolated amino compounds showed no biological activity; the nitro derivatives inhibited the growth of Neurospora crassa ATCC 9276, though not as effective as pyrrolnitrin itself. 2-Carboxy-4-(2-amino-3-bromophenyl)pyrrole (X) is demonstrated to be an intermediate in the biosynthesis of brominated pyrrolnitrin; the biosynthetic pathway to bromo derivatives of pyrrolnitrin is discussed.

The metabolism of tryptophan and 7-chlorotryptophan in Pseudomonas pyrrocinia and Pseudomonas aureofaciens

Pseudomonas pyrrocinia ATCC 15958 and a mutant strain (ACN) of Pseudomonas aureofaciens ATCC 15926 possess a mechanism for the degradation of the tryptophan side chain. Indole, indole-3-carboxylic acid, indole-3-acetic acid and the corresponding compounds chlorinated or brominated at position 7, as well as indole-3-pyruvate and 7-chloroindole-3-pyruvate, were isolated from bacterial cultures. The chlorinated indole derivatives were isolated after the addition of 7-chloro-DL-tryptophan to cultures of P. pyrrocinia whereas their bromo analogues were found in the culture medium of the mutant strain ACN of P. aureofaciens, grown in the presence of sodium bromide. Enzymatic studies show that tryptophan is transaminated to indole-3-pyruvate, which is transformed to indole-3-acetaldehyde. Dehydrogenation of indole-3-acetaldehyde leads to indole-3-acetic acid, which is further metabolized to indole-3-carboxaldehyde, and converted by dehydrogenation to indole-3-carboxylic acid. Indole is formed by the spontaneous decarboxylation of indole-3-carboxylic acid.