A variety of catalases and bromoperoxidases in genus Pseudomonas and their characterization

Plasmid pUPI126-encoded pyrrolnitrin production by Acinetobacter haemolyticus A19 isolated from the rhizosphere of wheat

An Acinetobacter species identified as A. haemolyticus A19 produces an antibiotic and the enzyme chitinase. The antibiotic produced by A. haemolyticus A19 was extracellular and inducible by co-cultivation with Klebsiella pneumoniae in the optimum ratio 2:1, respectively. pH 7, temperature 28 °C, and addition of 2% (w/v) NaCl are the most suitable environmental conditions for production and activity of the antibiotic. The antibiotic was produced in the early stationary growth phase (48 h) of A. haemolyticus A19. It has a very broad spectrum of antimicrobial activity against plant and human pathogenic bacteria and fungi. The antibiotic was extracted with ethyl acetate and purified by column chromatography with further purification by preparative thin-layer chromatography. Yield of the antibiotic was 15 mg/l. The antibiotic was active at very low concentrations, for example 50 μg/ml, and was water-soluble. It was stable at room temperature for up to 7 days. (1)H NMR analysis revealed the antibiotic was a pyrrolnitrin. It was found that pyrrolnitrin production by A. haemolyticus A19 was encoded by plasmid pUPI126 of molecular weight 25.7 kb. Plasmid pUPI126 was transferred to E. coli HB101 at a frequency of 5 × 10(-5) per μg DNA. It was also conjugally transformed to E. coli HB101 rif (r) mutants at a frequency of 5.9 × 10(-8) per recipient cell. Plasmid pUPI126 was 100% stable in Acinetobacter and 95% stable in E. coli HB101. Transconjugants and transformants both produced the antibiotic. This is the first report of plasmid-mediated pyrrolnitrin production by A. haemolyticus A19 isolated from wheat rhizosphere.

The crystal structure of a (-) gamma-lactamase from an Aureobacterium species reveals a tetrahedral intermediate in the active site

The structure of the recombinant (-) gamma-lactamase from an Aureobacterium species has been solved at 1.73A resolution in the cubic space group F23 with unit cell parameters a=b=c=240.6A. The trimeric enzyme has an alpha/beta hydrolase fold and closely resembles the cofactor free haloperoxidases. The structure has been solved in complex with a covalently bound ligand originating from the host cell and also in the unligated form. The associated density in the former structure has been interpreted as the two-ring ligand (3aR,7aS)-3a,4,7,7a-tetrahydro-benzo [1,3] dioxol-2-one which forms a tetrahedral complex with OG of the catalytic Ser98. Soaks of these crystals with the industrial substrate gamma-lactam or its structural analogue, norcamphor, result in the displacement of the ligand from the enzyme active site, thereby allowing determination of the unligated structure. The presence of the ligand in the active site protects the enzyme from serine hydrolase inhibitors. Cyclic ethylene carbonate, the first ring of the ligand, was shown to be a substrate of the enzyme.

Natural halogenated fatty acids: their analogues and derivatives

A comprehensive survey has been made of all fatty acids containing halogen atoms covalently bonded to carbon and which are deemed as naturally occurring. Generally thought to be minor components produced by many different organisms, these interesting compounds now number more than 300. Recent research, especially in the marine area, indicates this number will increase in the future. Sources of halogenated fatty acids include microorganisms, algae, marine invertebrates, and higher plants and some animals. Their possible biological significance has also been discussed

Reaction mechanism of the Co2+-activated multifunctional bromoperoxidase-esterase from Pseudomonas putida IF-3

The reaction mechanism of the Co2+-activated bromoperoxidase-esterase of Pseudomonas putida IF-3 was studied. Site-directed mutagenesis suggested that the serine residue of the catalytic triad conserved in serine hydrolases participates in the bromination and ester hydrolysis reactions. The enzyme released a trace amount of free peracetic acid depending on the concentration of H2O2, which had been considered the intermediate in the reaction of nonmetal haloperoxidases to oxidize halide ions to hypohalous acid. However, the formation of free peracetic acid could not explain the enzyme activation effect by Co2+ ions which completely depleted the free peracetic acid. In addition, the kcat value of the enzymatic bromination was 900-fold higher than the rate constant of free peracetic acid-mediated bromination. Those results strongly suggested that the peracetic acid-like intermediate formed at the catalytic site is the true intermediate and that the formation of free peracetic acid is only a minor reaction involving the enzyme. We propose the possible reaction mechanism of this multifunctional enzyme based on these findings.

Purification and characterization of a novel bromoperoxidase-catalase isolated from bacteria found in recycled pulp white water

A bacterial strain, Pseudomonad EF group 70B, containing a high catalase-like activity was found in process water (white water) from pulp using recycled fibers. The enzyme was purified and characterized, and found to be a hydroperoxidase. The active enzyme has an apparent molecular mass of about 153 kDa with two identical subunits and a pI value of 4.7. It has a rather sharp pH optimum for catalase activity at 6.0 but exhibits catalase, peroxidase and brominating activities over a broad pH range from 4 to 8. It was not inhibited by 3-amino-1,2,4-triazole. Peroxidase-like activity was found when adding o-dianisidine, pyrogallol, guaiacol and 4-aminoantipyrine. Brominating activity was noticed using monochlorodimedone as a substrate. The absorption spectrum exhibited a Soret band at 404 nm. Upon reduction with dithionite the Soret peak decreased and shifted to 436 nm. Pyridine hemochrome spectra indicated the presence of a protophorfyrin IX heme group and the enzyme was inhibited by the known heme ligands cyanide and azide. N-terminal amino acid analysis gave the sequence STEVKLPYAVAGGGTTILDAFPGE, which showed no homology with those of known catalases or peroxidases. It is concluded that the enzyme is a novel type of catalase-peroxidase or, more specifically, a bromoperoxidase-catalase, and that future developments of inhibitors of hydrogen peroxide-degrading activities in white water may be based on this enzyme and other catalase-peroxidases.

Cloning and biochemical characterization of Co(2+)-activated bromoperoxidase-esterase (perhydrolase) from Pseudomonas putida IF-3 strain

The gene encoding Co(2+)-activated bromoperoxidase (BPO)-esterase (EST), catalyzing the organic acid-assisted bromination of some organic compounds with H2O2 and Br(-) and quite specific hydrolysis of (R)-acetylthioisobutyric acid methyl ester, was cloned from the chromosomal DNA of the Pseudomonas putida IF-3 strain. The bpo-est gene comprises 831 bp and encoded a protein of 30181 Da. The enzyme was expressed at a high level in Escherichia coli and purified to homogeneity by ammonium sulfate fractionation and two-step column chromatographies. The recombinant enzyme required acetic acid, propionic acid, isobutyric acid or n-butyric acid in addition to H2O2 and Br(-) for the brominating reaction and was activated by Co(2+) ions. It catalyzed the bromination of styrene and indene to give the corresponding racemic bromohydrin. Although the enzyme did not release free peracetic acid in the reaction mixture, chemical reaction with peracetic acid could well explain such enzymatic reactions via a peracetic acid intermediate. The results indicated that the enzyme was a novel Co(2+)-activated organic acid-dependent BPO (perhydrolase)-EST, belonging to the non-metal haloperoxidase-hydrolase family.

Notomastus lobatus chloroperoxidase and Amphitrite ornata dehaloperoxidase both contain histidine as their proximal heme iron ligand

Two novel heme-containing peroxidases, one able to incorporate halogens into aromatic substrates and the other able to remove them, have recently been isolated from marine sources and initially characterized by Chen et al. [(1991) J. Biol. Chem. 266, 23909-23915; (1996) J. Biol. Chem. 271, 4609-4612]. The haloperoxidase Notomastus lobatus chloroperoxidase (NCPO) is unusual in requiring a flavoprotein component for peroxidase activity. The dehaloperoxidase (DHP), isolated from Amphitrite ornata, is the only heme-containing peroxide-dependent dehalogenase known to be capable of removing halogens including fluorine. Both enzymes are also quite atypical in that the molecular weights of their heme-containing subunits are less than 16,000, approximately one-half to one-fifth the size of typical heme-containing peroxidases. Interestingly, we have also found that both enzymes are isolated in their oxyferrous states even though all protein purification was done in the absence of any reductant. In the present study, we have examined these two enzymes with magnetic circular dichroism and UV-visible absorption spectroscopy in order to determine the identity of their proximal heme iron ligand. Four derivatives of each enzyme, cyanoferric, deoxyferrous, oxyferrous, and (carbonmonoxy)ferrous, have been examined and spectroscopically compared to parallel derivatives of myoglobin, a well-studied histidine-ligated heme protein. The spectra observed for each derivative of the two new enzymes are very similar to each other and, in turn, to the spectra of the same derivatives of myoglobin. We conclude that both new heme enzymes contain histidine as their proximal heme iron ligand. This makes NCPO the first histidine-ligated heme-containing peroxidase capable of chlorinating halogen acceptor substrates using chloride as the halogen donor. Further, the novel reactivity of DHP is not the result of an unusual proximal ligand. The present results with NCPO and DHP challenge the current dogma of how heme-containing peroxidases function: one chlorinates substrates without having a thiolate proximal ligand, and the other both oxygenates and dehalogenates haloaromatics and yet has a histidine proximal ligand like numerous other peroxidases that are not capable of such a combined reactivity.

Purification and characterization of a novel metal-containing nonheme bromoperoxidase from Pseudomonas putida

A novel bromoperoxidase was purified to homogeneity from the bacterium Pseudomonas putida IF-3 strain, which produces the antibiotic pyrrolnitrin. The enzyme had a molecular mass of 68,000 and was composed of two identical subunits (33,000). It was specific for I- and Br- and inactive toward Cl- and F- in the monochlorodimedone assay system. The optimum pH of the enzyme was around 4.2 and it rapidly lost its activity below 3.5, but it was stable over of range pH of 4 to 11. The purified enzyme was activated several fold by incubation with only cobalt ions, and did not contain an organic prosthetic group such as heme, flavin and cobalamin. Analyses of prosthetic metal compounds in the enzyme using plasma atomic emission spectroscopy (ICP-AES) combined with mass-spectroscopy (MS) and trace metal determination by high performance liquid chromatography (HPLC)-spectrometry, revealed that the enzyme contained 0.35 +/- 0.1 mol of cobalt ions, 1.0 +/- 0.2 mol of nickel ions, 0.8 +/- 0.2 mol of zinc ions and 2.0 +/- 0.2 mol of ferric iron per mol of enzyme, assuming the molecular weight of 68,000. There was no trace of vanadium in the enzyme, unlike in some nonheme haloperoxidases. Thus the bromoperoxidase of P. putida is a novel nonheme metal-containing bromoperoxidase.