Glycine Betaine Monooxygenase, an Unusual Rieske-Type Oxygenase System, Catalyzes the Oxidative N-Demethylation of Glycine Betaine in Chromohalobacter salexigens DSM 3043.

Although some bacteria, including Chromohalobacter salexigens DSM 3043, can use glycine betaine (GB) as a sole source of carbon and energy, little information is available about the genes and their encoded proteins involved in the initial step of the GB degradation pathway. In the present study, the results of conserved domain analysis, construction of in-frame deletion mutants, and an in vivo functional complementation assay suggested that the open reading frames Csal_1004 and Csal_1005, designated bmoA and bmoB, respectively, may act as the terminal oxygenase and the ferredoxin reductase genes in a novel Rieske-type oxygenase system to convert GB to dimethylglycine in C. salexigens DSM 3043. To further verify their function, BmoA and BmoB were heterologously overexpressed in Escherichia coli, and 13C nuclear magnetic resonance analysis revealed that dimethylglycine was accumulated in E. coli BL21(DE3) expressing BmoAB or BmoA. In addition, His-tagged BmoA and BmoB were individually purified to electrophoretic homogeneity and estimated to be a homotrimer and a monomer, respectively. In vitro biochemical analysis indicated that BmoB is an NADH-dependent flavin reductase with one noncovalently bound flavin adenine dinucleotide (FAD) as its prosthetic group. In the presence of BmoB, NADH, and flavin, BmoA could aerobically degrade GB to dimethylglycine with the concomitant production of formaldehyde. BmoA exhibited strict substrate specificity for GB, and its demethylation activity was stimulated by Fe2+ Phylogenetic analysis showed that BmoA belongs to group V of the Rieske nonheme iron oxygenase (RO) family, and all the members in this group were able to use quaternary ammonium compounds as substrates.IMPORTANCE GB is widely distributed in nature. In addition to being accumulated intracellularly as a compatible solute to deal with osmotic stress, it can be utilized by many bacteria as a source of carbon and energy. However, very limited knowledge is presently available about the molecular and biochemical mechanisms for the initial step of the aerobic GB degradation pathway in bacteria. Here, we report the molecular and biochemical characterization of a novel two-component Rieske-type monooxygenase system, GB monooxygenase (BMO), which is responsible for oxidative demethylation of GB to dimethylglycine in C. salexigens DSM 3043. The results gained in this study extend our knowledge on the catalytic reaction of microbial GB degradation to dimethylglycine.

4,6-Dinitro-o-cresol uncouples oxidative phosphorylation and induces membrane permeability transition in rat liver mitochondria.

The effect of the herbicide 4,6-dinitro-o-cresol (DNOC), a structural analogue of the classical protonophore 2,4-dinitrophenol, on the bioenergetics and inner membrane permeability of isolated rat liver mitochondria was studied. We observed that DNOC (10-50 microM) acts as a classical uncoupler of oxidative phosphorylation in rat liver mitochondria, promoting both an increase in succinate-supported mitochondrial respiration in the presence or absence of ADP and a decrease in transmembrane potential. The protonophoric activity of DNOC was evidenced by the induction of mitochondrial swelling in hyposmotic K(+)-acetate medium, in the presence of valinomycin. At higher concentrations (> 50 microM), DNOC also induces an inhibition of succinate-supported respiration, and a decrease in the activity of the succinate dehydrogenase can be observed. The addition of uncoupling concentrations of DNOC to Ca(2+)-loaded mitochondria treated with Ruthenium Red results in non-specific membrane permeabilization, as evidenced by mitochondrial swelling in isosmotic sucrose medium. Cyclosporin A, which inhibits mitochondrial permeability transition, prevented DNOC-induced mitochondrial swelling in the presence of Ca2+, which was accompanied by a decrease in mitochondrial membrane protein thiol content, owing to protein thiol oxidation. Catalase partially inhibits mitochondrial swelling and protein thiol oxidation, indicating the participation of mitochondrial-generated reactive oxygen species in this process. It is concluded that DNOC is a potent potent protonophore acting as a classical uncoupler of oxidative phosphorylation in rat liver mitochondria by dissipating the proton electrochemical gradient. Treatment of Ca(2+)-loaded mitochondria with uncoupling concentrations of DNOC results in mitochondrial permeability transition, associated with membrane protein thiol oxidation by reactive oxygen species.

Resistance to nitrophenolic herbicides and metronidazole in the cyanobacterium Synechocystis sp. PCC 6803 as a result of the inactivation of a nitroreductase-like protein encoded by drgA gene.

Dinoseb is a herbicide known to inhibit photosystem II electron transfer like DCMU, triazine and phenolic-type herbicides. The mutant Din7 of the cyanobacterium Synechocystis sp. PCC 6803, selected for resistance to dinoseb, and the mutant Ins2, constructed by the insertion of the kanamycin resistance cassette into the drgA gene, were cross-resistant to other nitrophenolic herbicides (DNOC, 2,4-dinitrophenol) and to the cell inhibitor metronidazole but not to the photosystem II inhibitors DCMU or ioxynil. The Din7 mutant had the same characteristics of photosystem II inhibition by dinoseb as the wild type. This result suggested the existence of another site for dinoseb inhibition. The wild type cells modified dinoseb to a non-toxic product that gave an absorption spectrum similar to that of dithionite treated dinoseb containing reduced nitro groups. In contrast, the Din7 mutant did not modify dinoseb. These phenomena were controlled by the drgA gene encoding a protein which showed similarity to several enzymes having nitroreductase activity. The addition of superoxide dismutase to the medium relieved the toxic effect of dinoseb in wild type cells but not in Din7. It is proposed that in wild type cells of Synechocystis sp. PCC 6803 the DrgA protein is involved in detoxification of dinoseb via the reduction of the nitro group(s) and this process is accompanied by the formation of toxic superoxide anions. Mutations blocking the activity of the DrgA protein lead to the development of resistance to nitrophenolic herbicides and metronidazole.

Effect of polychlorinated biphenyls on drug metabolism in Japanese quail and its progeny.

PCB (DP5, 1 and 5 mg/female/day, orally for 40 days) induce microsomal hepatic enzymes (cytochrome P-450, aniline hydroxylase, aldrin epoxidase, p-nitroanisole demethylase, p-nitrophenol: UDPGA-transferase) in adult female Japanese quail. Toxicity of dinitro-o-cresol (DNOC) is reduced in treated animals. High hepatic activity occurs in young quails issued from treated females, but closely related to residue levels, normal enzyme activities are reestablished within 1 month.

[Morpho-functional state of biomembranes after treatment with alkyl derivatives of 2,4-dinitrophenol]. / Morfofunktsional'noe sostoianie biomembran pri vozdeistvii alkilproizvodnykh 2,4-dinitrofenola.

The morphofunctional state of the rat liver biomembranes is studied under conditions of the peroral effect of alkyl dinitrophenols: dinitroorthocresole and secondary 2,4-dinitro-6-butylphenol. It is established that free radicals and products of peroxide lipid oxidation (diene conjugates, hydroperoxides, final products reacting with 2-thiobarbituric acid) are very important for realization of the membrane-tropic action of the above compounds. Possible mechanisms of development of the membrane-damaging action of these xenobiotics and their effect on the state of the mitochondrial respiratory chain are discussed. The membrane-tropic effect of alkyl dinitrophenols is confirmed by the results of electron-microscopic studies.

[Dinitroorthocresol dissociation of oxidative phosphorylation in the rat liver perfused in situ]. / Roz'iadnannia okysniuval'noho fosforyliuvannia dynitroortokrezolom u perfuzovanii in situ pechintsi shchuriv

Perfusion of the rat liver in situ for 150 min provides for maintaining optimal values of acid-base balance for the following indexes: surplus of bases, content of standard bicarbonate, buffer bases pH, pO2, pCO2, HbO2, the level of bile secretion, content of lactate, pyruvate, ATP, ADP, that evidences for a high functional activity in the tissue. Introduction of dinitro-ortho-cresol (DNC) into the perfusion liquid causes development of acidosis. DNC results in dissociation of oxidative phosphorylation: the content of ATP and intensity of inorganic phosphorus utilization decrease, oxygen uptake intensifies. A compensatory increase in the glycolysis intensity directed to maintaining the level of macroergs under these conditions is is pronounced in the intensified uptake of glucose, in a rise in the content of lactate in perfusate and an increase in the pyruvate kinase activity in the liver. The redox state of NAD-pairs (ratio of [NAD+] : [NADN] calculated from the content of redox metabolites and the equilibrium constant for the lactate dehydrogenase system shifts toward an increase in the reducing properties of hepatocytes cytoplasm. The phosphate potential value calculated from the ratio [ATP] : [ADP] - [Pinor] lowers under conditions of the experiment.