Mercury and organomercurial degrading enzymes in a broad-spectrum Hg-resistant strain of Bacillus pasteurii
01 Apr 1994-Bulletin of Environmental Contamination and Toxicology (Springer-Verlag)-Vol. 52, Iss: 4, pp 582-589
About: This article is published in Bulletin of Environmental Contamination and Toxicology.The article was published on 1994-04-01. It has received 4 citations till now. The article focuses on the topics: Mercury(II) reductase.
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01 Jan 1998
TL;DR: In this article, the authors describe the properties of Hg such as its tendency to form highly stable complexes and compounds (including species that are easily taken up by organisms but not readily excreted), natural processes (e.g. methylation) which enhance the bioavailability of HGs, increased bioavailability due to environmental changes caused by human activities, and efficient accumulation of Hgs by organisms and certain natural materials, such as soil organic matter and fine-grained sediments.
Abstract: Mercury (Hg) is one of the most toxic heavy metals. From a biological perspective it has no redeeming virtue, for, unlike a number of other heavy metals, it is not known to perform any essential biochemical function (Bowen, 1966). Traces of Hg are ubiquitous in soils, natural waters, sediments, organisms and air (Jonasson and Boyle, 1972), and anomalously high Hg concentrations occur in many ecosystems owing to Hg pollution (a serious, widespread problem), natural Hg enrichment in certain rocks, distinctive properties of Hg such as its tendency to form highly stable complexes and compounds (including species that are easily taken up by organisms but not readily excreted), natural processes (e.g. methylation) which enhance the bioavailability of Hg, increased bioavailability of Hg due to environmental changes caused by human activities, and efficient accumulation of Hg by organisms and certain natural materials, such as soil organic matter and fine-grained sediments. Moreover, Hg is a relatively volatile element, and this accounts, in large part, for its wide distribution.
116 citations
TL;DR: Immobilized mercury-resistant bacterial cells of Azotobacter chroococcum could effectively volatilize mercury from mercury-containing buffer and detoxify mercury compounds and the storage stability of immobilized cells was much better than that of the native cells.
Abstract: Highly toxic mercury compounds may come into the environment through the use of mercury compounds as disinfectants for hospital and household purposes, Hg catalyst in industries, burning of coal and petroleum products, mercury-based pesticides and fungicides used in agriculture, and seed dressings. Toxic effects of mercury can be counteracted by microbial cells through the enzymes mercuric reductase and organomercurial lyase. Immobilized mercury-resistant bacterial cells of Azotobacter chroococcum could effectively volatilize mercury from mercury-containing buffer and detoxify mercury compounds. Moreover, the efficiency of mercury volatilization was much greater than with the native cells, as immobilized cells can be reused. Immobilized cells continuously volatilized mercury from mercury-containing buffer after four consecutive 24 h cycles. The storage stability of immobilized cells was much better than that of the native cells.
13 citations
TL;DR: Flavobacterium rigense strain PR2, a broad-spectrum mercury-resistant bacterium abundantly present in soil exhibited multiple metal resistance properties due to the sequential action of two mercury-detoxicating enzymes, organomercurial lyase and mercuric reductase.
Abstract: Flavobacterium rigense strain PR2, a broad-spectrum mercury-resistant bacterium abundantly present in soil exhibited multiple metal resistance properties. Mercury resistance was due to the sequential action of two mercury-detoxicating enzymes, organomercurial lyase and mercuric reductase. The levels of these enzyme activities were determined using different mercury compounds as inducers and substrates. Mercuric reductase was partially purified from the bacterium and the physicochemical properties of the enzyme were studied. The effect of several enzyme inhibitors and heavy metal ions on the enzyme activity was also studied.
8 citations
TL;DR: Five nitrogen-fixing Azotobacter strains isolated from agricultural farms in West Bengal, India, were resistant to mercuric ion and organomercurials and NADPH and GSH might have a role in suppressing the inhibition of N 2 -fixation in the presence of Hg compounds.
Abstract: Five nitrogen-fixing Azotobacter strains isolated from agricultural farms in West Bengal, India, were resistant to mercuric ion and organomercurials. Resistance of Hg-resistant bacteria to mercury compounds is mediated by the activities of mercuric reductase and organomercurial lyase in the presence of NADPH and GSH as cofactors. These bacteria showed an extended lag phase in the presence of 10-50 μmol l -1 HgCl 2 . Nitrogen-fixing ability of these isolates was slightly inhibited when the mercury-resistant bacterial cells were preincubated with 10 μmol l -1 HgCl 2 . Acetylene reduction by these bacteria was significantly inhibited (91-97%) by 50 μmol l -1 HgCl 2 . However, when GSH and NADPH were added to the acetylene reduction assay mixture containing 50 nmol l -1 HgCl 2 , only 42-50% inhibition of nitrogenase activity was observed. NADPH and GSH might have a role in suppressing the inhibition of N 2 -fixation in the presence of Hg compounds either by assisting Hg-detoxifying enzymes to lower Hg concentration in the assay mixture or by formation of adduct comprising Hg and GSH which is unable to inhibit nitrogen fixation.
7 citations
References
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TL;DR: Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
Abstract: Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins, a number of modified analytical procedures utilizing this reagent have been reported for the determination of proteins in serum, in antigen-antibody precipitates, and in insulin. Although the reagent would seem to be recommended by its great sensitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard to effects of variations in pH, time of reaction, and concentration of reactants, permissible levels of reagents commonly used in handling proteins, and interfering substances. Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
289,852 citations
TL;DR: The mercury cycle in the biosphere and biological methylation of mercury and microbial resistance to mercury and organomercurials are studied.
Abstract: BIOTRANSFORMA nONS OF TOXIC MET AL CAnONS . Mercury . The mercury cycle in the biosphere .. Biological methylation of mercury . Microbial resistance to mercury and organomercurials .
413 citations
"Mercury and organomercurial degradi..." refers background in this paper
...Hg-resistant bacteria are known to possess plasmids which code for the induced synthesis of HgZ+-reductase (MR) and organomercurial lyase (OL) ( Summers and Silver 1978, Silver and Misra 1988)....
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TL;DR: The search for the “missing link” in the mechanism of Mercury’s reprograming continues to be a major challenge.
Abstract: INTRODUCTION...... . . . . .... . . . . . . . . . . . . . . . . . .. ...... . . . . . . . . . . . .... . . . .. ........ .. . 607 Occurrena of Mercury in the Environment 607 Incidence of the Mercury Resistance Phenotype 608 THE GRAM-NEGATIVE SySTEMS 609 The Structural Genes of the mer Loci 609 Regulation ...... . 618 Overview of Operon Function........ . . .. . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . .... . . . . .. . . . .. . . . . . . . . . 623 .. Evolutionary Considerations ... . . . ........ . . . . . . . . . . . . . . . . ..... . . . . . . . . ....... . . . . . . 624 THE GRAM-POSITIVE SySTEMS 626 Occurrence . . . " 626 Biochemistry.. . . . . 627 Genetics . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 CONCLUDING REMARKS 627
330 citations
TL;DR: The method is applicable to measurement of flavin concentrations in the nanomolar range and can be readily used for determination of the flavin composition of purified flavoproteins.
Abstract: A rapid fluorometric method for the determination of FMN and FAD concentrations in mixtures of the two compounds is described. The method is applicable to measurement of flavin concentrations in the nanomolar range. It can be readily used for determination of the flavin composition of purified flavoproteins.
275 citations
TL;DR: It was shown that mercuric reductase has the capacity to accept four electrons per FAD-containing subunit, and that two thiols become kinetically titrable by 5,5'-dithiobis-(2-nitrobenzoate) upon reduction with NADPH, characteristic features of the disulfide reduct enzyme class of flavoproteins.
Abstract: The flavoprotein mercuric reductase catalyzes the two-electron reduction of mercuric ions to elemental mercury using NADPH as an electron donor. It has now been purified from Pseudomonas aeruginosa PAO9501 carrying the plasmid pVS1. In this plasmid system, where the mer operon is on the transposon Tn501, mercuric reductase comprises up to 6% of the soluble cellular protein upon induction with mercurials. The purification is a rapid (two-step), high yield (80%) procedure. Anaerobic titrations of mercuric reductase with dithionite revealed the formation of a charge transfer complex with an absorbance maximum around 540 nm. Striking spectroscopic similarities to lipoamide dehydrogenase and glutathione reductase were observed. These two enzymes, which catalyze the transfer of electrons between pyridine nucleotides and disulfides, are flavoproteins which contain an oxidation-reduction-active cysteine residue at the active site. The expectation that mercuric reductase contains a similar electron acceptor was confirmed when it was shown that mercuric reductase has the capacity to accept four electrons per FAD-containing subunit, and that two thiols become kinetically titrable by 5,5'-dithiobis-(2-nitrobenzoate) upon reduction with NADPH. These are characteristic features of the disulfide reductase class of flavoproteins. Further similarities with at least one of these enzymes, lipoamide dehydrogenase, include the E/EH2 midpoint potential (-269 mV), fluorescence properties, and extinction coefficients of E and EH2. Preliminary observations relevant to an understanding of the mechanism of mercuric reductase are discussed.
256 citations