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138 records · Page 8Linked to original sources
PubMed1992

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

A survey of bromoperoxidase in some Pseudomonas strains revealed that they contain different types of bromoperoxidase, catalase-bromoperoxidase and catalase. Although all Pseudomonas strains exhibited catalase activity, the enzyme isolated from P. pyrrolnitrica was named catalase-bromoperoxidase, because it catalyzed not only a catalase reaction, but also the bromination of monochlorodimedone. Except heme-type catalase-bromoperoxidase, this strain contained four isoenzymes of general nonheme bromoperoxidase, and their molecular weights were about 73,000. On the other hand, P. putida and P. aeruginosa had the usual heme-type catalase, but they differed in molecular weight and pI value. Both strains also had a nonheme bromoperoxidase which catalyzed the bromination of monochlorodimedone and aniline, and the molecular weight of each enzyme was 68,000 for P. putida and 86,000 for P. aeruginosa. Considering the results reported by Van Pée et al. [1] and Weisner et al. [2], regarding the haloperoxidases of Pseudomonas, the genus was revealed to contain a wide variety of bromoperoxidase and catalase.

Catalase↗
PubMed2006

Recent developments in enzymatic chlorination.

While the existence of chlorinated natural products has been known for over 100 years, our understanding of the enzymology of biological chlorination reactions has been limited to chloroperoxidases, which are now known not to play a significant role in chlorometabolite biosynthesis. The discoveries of new classes of halogenases, described in this Highlight, have shed new light on the mechanisms of enzymatic chlorination of aromatic and aliphatic compounds.

Biological Products↗
PubMed2004

Crystallization and X-ray diffraction of a halogenating enzyme, tryptophan 7-halogenase, from Pseudomonas fluorescens.

Chlorination of natural products is often required for their biological activity; notable examples include vancomycin, the last-ditch antibiotic. It is now known that many chlorinated natural products are made not by haloperoxidases, but by FADH2-dependent halogenases. The mechanism of the flavin-containing enzymes is obscure and there are no structural data. Here, crystals of PrnA (tryptophan 7-halogenase), an enzyme that regioselectively chlorinates tryptophan, cocrystallized with tryptophan and FAD are reported. The crystals belong to the tetragonal space group P4(3)2(1)2 or P4(1)2(1)2, with unit-cell parameters a = b = 67.8, c = 276.9 A. A data set to 1.8 A with 93% completeness and an Rmerge of 7.1% has been collected from a single flash-cooled crystal. A method for incorporating selenomethionine in a Pseudomonas fluorescens expression system also is reported.

Crystallization↗
PubMed1998

Halogenation of aromatic compounds: thermodynamic, mechanistic and ecological aspects.

Biological halogenation of aromatic compounds implies the generation of reducing equivalents in the form of e.g. NADH. Thermodynamic calculations show that coupling the halogenation step to a step in which the reducing equivalents are oxidized with a potent oxidant such as O2 or N2O makes the halogenation reaction thermodynamically feasible without the input of additional energy in the form of e.g. NADH. In a current model on the halogenation of tryptophan to 7-chloro-L-tryptophan NADH and O2 are proposed as co-substrates in a reaction in which the aromatic compound is oxidized via an epoxide as intermediate. The thermodynamic calculations thus indicate that such a route hinges on mechanistic insights but has no thermodynamic necessity. Furthermore the calculations suggest that halogenation of tryptophan and other aromatic compounds should be possible with N2O, and possibly even with nitrate replacing O2 as the oxidant.

Antifungal Agents↗
PubMed2006

Probing the substrate specificity of aminopyrrolnitrin oxygenase (PrnD) by mutational analysis.

Molecular modeling and mutational analysis (site-directed mutagenesis and saturation mutagenesis) were used to probe the molecular determinants of the substrate specificity of aminopyrrolnitrin oxygenase (PrnD) from Pseudomonas fluorescens Pf-5. There are 17 putative substrate-contacting residues, and mutations at two of the positions, positions 312 and 277, could modulate the enzyme substrate specificity separately or in combination. Interestingly, several of the mutants obtained exhibited higher catalytic efficiency (approximately two- to sevenfold higher) with the physiological substrate aminopyrrolnitrin than the wild-type enzyme exhibited.

Amines↗
PubMed1996

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.

Bacteria↗