Mercury binding to proteins disclosed by ESI MS experiments: The case of three organomercurials.

Solution interactions of three organomercury compounds, i.e., methylmercury chloride, thimerosal and phenylmercury acetate, with a group of biochemically relevant proteins, namely cytochrome c (Cyt c), ribonuclease A (RNase A), carbonic anhydrase I (hCA I), superoxide dismutase (SOD), and serum albumin (HSA), were investigated using an established ESI MS approach. Temporal analysis of sample aliquots provided insight into the binding kinetics, while comparative analysis of the obtained mass spectra disclosed adduct formation of each mercurial with the tested proteins and the relative abundance of the species. The three organomercurials bind, exclusively and tightly, to free cysteine residues as no binding was observed in the case of proteins lacking such groups. hCA I, SOD and HSA formed distinct mercury adducts, preserving the Hg bound alkyl/aryl ligands; yet, the three organomercurials displayed significant differences in reactivity in relation to their chemical structure. The investigation was then extended to analyze the reactions with the C-terminal dodecapeptide of the enzyme human thioredoxin reductase, which contains a characteristic selenol-thiol moiety: tight Hg binding was observed. Notably, this peptide was able to remove effectively and completely the alkyl/aryl ligands of the three tested organomercurials; this behavior may be relevant to the detoxification mechanism of organomercurials in mammals. Finally, a competition experiment was carried out to establish whether protein bound mercury centers may be displaced by other competing metals. Interestingly, and quite unexpectedly, we observed that a protein bound mercury fragment may be partially displaced from its coordination site in hCA I by the medicinal gold compound auranofin.

Variants in HNRNPH1 are associated with high myopia in humans and ocular coloboma in zebrafish.

High myopia is one of the most common causes for blindness due to its associated complications. Genetic factor has been considered as the major cause for early-onset high myopia (eoHM), but exact genetic defects for most eoHM are yet to be identified. Through multi-step bioinformatics analysis of our in-house whole exome sequencing dataset from 6397 individuals, variants from 928 probands with eoHM were further compared with those from in-house controls as well as gnomAD database. The results showed that loss-of-function (LoF) variants in a novel gene HNRNPH1 were identified in two of 928 probands with eoHM but in none of 5469 probands with other eye conditions (p = 0.02). LoF variants in HNRNPH1 were extremely rare and intolerant, while two LoF variants in 928 eoHM were statistically higher than their frequency in gnomAD (p = 5.98 × 10-4 ). These two LoF variants, c.2dup/p.(M1?) and c.121dup/p.(Q41Pfs*20), were absent from existing database. Variants in HNRNPH1 have not been associated with any inherited eye disease before. Expression of HNRNPH1 was enriched in ganglion cell layer and inner nuclear layer in humans. Knockdown of hnrnph1 in zebrafish resulted in ocular coloboma. All these suggest that HNRNPH1 is potential contribution to eoHM when mutated.

Covalent inhibition of P. falciparum ferredoxin-NADP+ reductase: Exploring alternative strategies for the development of new antimalarial drugs.

The protozoan Plasmodium falciparum is the main aetiological agent of tropical malaria. Characteristic of the phylum is the presence of a plastid-like organelle which hosts several homologs of plant proteins, including a ferredoxin (PfFd) and its NADPH-dependent reductase (PfFNR). The PfFNR/PfFd redox system is essential for the parasite, while mammals share no homologous proteins, making the enzyme an attractive target for novel and much needed antimalarial drugs. Based on previous findings, three chemically reactive residues important for PfFNR activity were identified: namely, the active-site Cys99, responsible for hydride transfer; Cys284, whose oxidation leads to an inactive dimeric form of the protein; and His286, which is involved in NADPH binding. These amino acid residues were probed by several residue-specific reagents and the two cysteines were shown to be promising targets for covalent inhibition. The quantitative and qualitative description of the reactivity of few compounds, including a repurposed drug, set the bases for the development of more potent and specific antimalarial leads.

The Irrawaddy dolphin, Orcaella brevirostris from the Mekong river Cambodia: Preliminary health and toxicological investigations.

The subpopulation of the Irrawaddy dolphin (Orcaella brevirostris) living in the Mekong River, Cambodia, is considered to be critically endangered. The aim of the investigation was to gain information about the genetic variation, health status and exposure to toxic compounds of these dolphins. Tissue samples from 27 Irrawaddy river dolphins found dead along the Mekong River between 2004 and 2009 were analysed with regards to genetics, pathology and ecotoxicology. Genetic maternal lineage detection, based on polymorphisms of the mitochondrial d-loop sequences, was performed. Data indicate a genetic separation of the Mekong dolphins from both the coastal population and the Mahakam dolphins. Pathological investigations revealed acute moderate multifocal suppurative bronchopneumonia, moderate periportal hepatic lipidosis, moderate diffuse hepatic atrophy and acute severe diffuse suppurative leptomeningitis. Residue levels of organochlorines and polybrominated diphenyl ethers in Irrawaddy dolphins from the Mekong River were lower than the concentrations reported for other cetaceans in the coastal and riverine waters of Asia, except for Dichlorodiphenyltrichloroethane. A high percentage of organic mercury compared to the immuno-toxic methylmercury was observed. Due to numerous confounding factors, it is not possible to relate levels of pollutants to observed morphological lesions. However, it is likely that chemical contaminants do adversely impact on the health of the Irrawaddy dolphins at present, and have also affected previous generations.

1,8-Dimercuri-6-Phenyl-1H-Carbazole as a Monofacial Dinuclear Organometallic Nucleobase.

A C-nucleoside with 6-phenyl-1H-carbazole as the base moiety has been synthesized and incorporated in the middle of an oligonucleotide. Mercuration of this modified residue at positions 1 and 8 gave the first example of an oligonucleotide featuring a monofacial dinuclear organometallic nucleobase. The dimercurated oligonucleotide formed stable duplexes with unmodified oligonucleotides placing either cytosine, guanine, or thymine opposite to the organometallic nucleobase. A highly stabilizing (ΔTm =7.3 °C) HgII -mediated base pair was formed with thymine. According to DFT calculations performed at the PBE0DH level of theory, this base pair is most likely dinuclear, with the two HgII ions coordinated to O2 and O4 of the thymine base.

Ion-induced PCR strategy for mercury detection.

Mercury contamination is one of the most serious environmental problems. It can cause serious effects on the human health, such as case damage in the brain, nervous system, immune system, and kidney failure. Therefore, development of an accurate, sensitive, and simple operational detection method for mercury is very necessary. Herein, we report a new strategy for mercury ion detection based on commonly used PCR technique. High selectivity and sensitivity were achieved by the formation of the thymine-Hg-thymine (T-Hg-T) unnatural base pair at the 3'-end of PCR primers. The detection results of PCR amplification in presence of mercury ion could be reported either by using agarose gel analysis or through real-time fluorometric dye tracing for different detection purposes. To our knowledge, this study represents the first application of PCR based technique to the detection of metal ions.

A highly-selective chloride microelectrode based on a mercuracarborand anion carrier.

The chloride gradient plays an important role in regulating cell volume, membrane potential, pH, secretion, and the reversal potential of inhibitory glycine and GABAA receptors. Measurement of intracellular chloride activity, [Formula: see text], using liquid membrane ion-selective microelectrodes (ISM), however, has been limited by the physiochemical properties of Cl- ionophores which have caused poor stability, drift, sluggish response times, and interference from other biologically relevant anions. Most importantly, intracellular [Formula: see text] may be up to 4 times more abundant than Cl- (e.g. skeletal muscle) which places severe constraints on the required selectivity of a Cl- - sensing ISM. Previously, a sensitive and highly-selective Cl- sensor was developed in a polymeric membrane electrode using a trinuclear Hg(II) complex containing carborane-based ligands, [9]-mercuracarborand-3, or MC3 for short. Here, we have adapted the use of the MC3 anion carrier in a liquid membrane ion-selective microelectrode and show the MC3-ISM has a linear Nernstian response over a wide range of aCl (0.1 mM to 100 mM), is highly selective for Cl- over other biological anions or inhibitors of Cl- transport, and has a 10% to 90% settling  time of 3 sec. Importantly, over the physiological range of aCl (1 mM to 100 mM) the potentiometric response of the MC3-ISM is insensitive to [Formula: see text] or changes in pH. Finally, we demonstrate the biological application of an MC3-ISM by measuring intracellular aCl, and the response to an external Cl-free challenge, for an isolated skeletal muscle fiber.

DNA engineered copper oxide-based nanocomposites with multiple enzyme-like activities for specific detection of mercury species in environmental and biological samples.

In this paper, we report the synthesis and application of enzyme-like DNA-copper oxide/platinum nanoparticles for the separate quantification of inorganic and organomercury species in various real samples. We synthesized a series of poly(thymine) (T60)-copper oxide/metal nanocomposites (T60-CuxO/M NCs; M = Au, Ag or Pt) that exhibited enzyme-like activities [oxidase (OX), peroxidase (POX), and catalase (CAT)]. The enzyme-like activities are tunable due to the incorporation of various metals into the NCs. Among a series of synthesized CuxO/M NCs, T60-copper oxide-platinum nanocomposites (T60-CuxO/Pt NCs) exhibited the highest OX-like activity via the O2-mediated oxidation of substrates, such as Amplex Red (AR), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), o-phenylenediamine (OPD), and 3,3',5,5'-tetramethylbenzidine (TMB), to form fluorescent or colored products. Interestingly, inorganic mercury ions (Hg2+) and organomercury species, such as methylmercury (MeHg+), ethylmercury (EtHg+), and phenylmercury (PhHg+), significantly inhibited the OX-like activity of T60-CuxO/Pt NCs. For the selective detection of mercury species, we used ABTS in the T60-CuxO/Pt NCs system, and the ABTS/T60-CuxO/Pt NCs-based assay allowed for the detection of mercury ions at nanomolar concentrations based on the decrease in the catalytic activity caused by the mercury ions. To separately quantify the inorganic and organomercury species in a sample, we employed selenium nanoparticles (Se NPs) as a masking agent, as they preferentially bind with inorganic mercury species. The ABTS/T60-CuxO/Pt NCs-based assay with the masking agent of Se NPs further provided specificity for the detection of organomercury species in environmental water samples (tap water, river water, and seawater) and fish muscle samples (dogfish muscle DORM-II).

Synthesis and application of ion-imprinted polymer for the determination of mercury II in water samples.

In this study, an innovative analytical methodology capable of selectively identifying and quantifying mercury contamination by the association of solid-phase extraction using ion-imprinted polymers as a sorbent phase and differential pulse anodic stripping voltammetry is proposed. To this end, the ion-imprinted polymers were synthesized and characterized by infrared spectroscopy and atomic force microscopy. The sorption capacities and the selectivity of the ion-imprinted polymers were compared to the ones related to the non-imprinted ones. Next, the experimental parameters of this solid-phase extraction method (IIP-SPE) were evaluated univariately. The selectivity of this polymeric matrix against other cations (Cd II, Pb II, and Cu II) was also evaluated. Limits of detection (LOD) and quantification (LOQ) obtained for the here proposed methodology were 0.322 µg L-1 and 1.08 µg L-1, respectively. Also, the precision of 4.0% was achieved. The method was finally applied to three water samples from different sources: for the Piratininga and Itaipu Lagoon waters, Hg II concentrations were below the LOQ and for Vargem River waters a concentration equal to 1.35 ± 0.07 mg L-1 was determined. These results were confirmed by recovery tests, resulting in a recovery of 96.2 ± 4.0%, and by comparison with flame atomic absorption spectrometry, resulting in statistical conformity between the two methods at 95% confidence level.

Auditory and Histopathological Effects of Topical Mercurochrome Treatment in Rats with Tympanic Membrane Perforation.

OBJECTIVES: Topical treatment is first choice in the treatment of uncomplicated chronic otitis media. It was intended to assess auditory and histopathological safety of ototopical use of mercurochrome solution in rats with induced tympanic membrane perforation. MATERIALS AND METHODS: The study was conducted on 21 female Wistar-Albino rats which were randomly assigned into 3 groups. In all rats, perforation was performed at right tympanic membrane. Distortion product otoacoustic emissions (DPOAEs) measurements were performed at frequencies of 2000, 3000 and 4000 Hz (with L1/L2: 70 /70 dB at 2f1-f2 frequency; f2/f1 ratio: 1:22) before recovery from anesthesia and signal-to-noise ratio (SNR) were recorded. Normal saline, 2% mercurochrome and gentamicin were given to group 1, 2 and 3 twice daily over a week, respectively. Rats were sacrificed after DPOAE measurements on day 14. Right temporal bone specimens were examined under light microscope after processing. RESULTS: Based on DPOAE results, there was no significant difference among groups before treatment. On day 14, significant differences were found in DPOAE measurements at 3000 and 4000 Hz, and in mean SNR values in 2% mercurochrome and gentamicin groups when compared to normal saline group while no significant difference was detected at 2000 Hz among groups. In addition, significant degeneration was detected in Corti organs, spiral ganglions and stria vascularis in groups 2 and 3. CONCLUSION: In this study, it was observed that mercurochrome use in external otitis and otitis media with tympanic membrane perforation could cause ototoxicity and concluded that the solution should be used cautiously.

Analysis of Cysteine Post Translational Modifications Using Organic Mercury Resin.

The wide reactivity of the thiol group enables the formation of a variety of reversible, covalent modifications on cysteine residues. S-nitrosylation, like many other post-translational modifications, is site selective, reversible, and necessary for a wide variety of fundamental cellular processes. The overall abundance of S-nitrosylated proteins and reactivity of the nitrosyl group necessitates an enrichment strategy for accurate detection with adequate depth. Herein, a method is presented for the enrichment and detection of endogenous protein S-nitrosylation from complex mixtures of cell or tissue lysate utilizing organomercury resin. Minimal adaptations to the method also support the detection of either S-glutathionylation or S-acylation using the same enrichment platform. When coupled with high accuracy mass spectrometry, these methods enable a site-specific level of analysis, facilitating the curation comparable datasets of three separate cysteine post-translational modifications. © 2018 by John Wiley & Sons, Inc.

Study of Lignin-Modified Silica Gel Adsorption after Association with Six Different Organophenylmercuric Compounds in Chloroform.

In this study, the adsorption of lignin-modified silica gel after association with six different organophenylmercuric compounds in chloroform was investigated. Adsorption reached approximately 90% of the maximum value within 15 min. The adsorption capacity, Fourier transform infrared spectroscopy, and interaction simulation results indicated that the adsorption proportion resulted from the strong dipole-dipole interaction between the lignin and analyte molecules, and was considered to be size- and structure-dependent. However, the π-π complexation interaction arising from the acidic aromatic moiety of the analyte, which was significant in an apolar environment, was not the major force responsible for the resulting adsorption. Additives, such as acid or ether, which competed with the analyte for the binding site on the lignin molecule, were not beneficial to the interaction, and thus not beneficial to the adsorption processes.

Revision of reciprocal action of mercury and selenium.

Diverse forms of mercury (Hg) have various effects on animals and humans because of a variety of routes of administration. Inorganic mercury (iHg) binds to thiol groups of proteins and enzymes in one's body or is methylated by microorganisms. Organic form of Hg, contrary to the iHg, is more stable but may be demethylated to Hg2+ in the tissue of intestinal flora. Selenium (Se) also occurs in a variety of chemical forms in one's body but both of these elements behave very differently from one another. Mercury binding to selenide or Se-containing ligands is a primary molecular mechanism that reduces toxicity of Hg. Complexes formed in such a way are irreversible, and thus, biologically inactive. Se deficiency in a human body may impair normal synthesis of selenoproteins and its expression because expression of mRNA may be potentially regulated by the Se status. This paper provides a comprehensive review concerning Hg-Se reciprocal action as a potential mechanism of protective action of Se against Hg toxicity as well as a potential detoxification mechanism. Although interactions between Hg-Se have been presented in numerous studies concerning animals and humans, we have focused mainly on animal models so as to understand molecular mechanisms responsible for antagonism better. The review also investigates what conclusions have been drawn by researchers with respect to the chemical species of Se and Hg (and their relationship) in biological systems as well as genetic variations and expression and/or activity of selenoproteins related to the thioredoxin (thioredoxin Trx/TrxR) system and glutathione metabolism. Int J Occup Med Environ Health 2018;31(5):575-592.

Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts.

Content of heavy metals, including mercury, determines the method of management and disposal of sewage sludge. Excessive concentration of mercury in composts used as organic fertilizer may lead to accumulation of this element in soil and plant material. Fractionation of mercury in sewage sludge and composts provides a better understanding of the extent of mobility and bioavailability of the different mercury species and helps in more informed decision making on the application of sludge for agricultural purposes. The experimental setup comprises the composing process of the sewage sludge containing 13.1mgkg-1 of the total mercury, performed in static reactors with forced aeration. In order to evaluate the bioavailability of mercury, its fractionation was performed in sewage sludge and composts during the process. An analytical procedure based on four-stage sequential extraction was applied to determine the mercury content in the ion exchange (water soluble and exchangeable Hg), base soluble (Hg bound to humic and fulvic acid), acid soluble (Hg bound to Fe/Mn oxides and carbonates) and oxidizable (Hg bound to organic matter and sulphide) fractions. The results showed that from 50.09% to 64.55% of the total mercury was strongly bound to organo-sulphur and inorganic sulphide; that during composting, increase of concentrations of mercury compounds strongly bound with organic matter and sulphides; and that mercury content in the base soluble and oxidizable fractions was strongly correlated with concentration of dissolved organic carbon in those fractions.

The aging kidney and the nephrotoxic effects of mercury.

Owing to advances in modern medicine, life expectancies are lengthening and leading to an increase in the population of older individuals. The aging process leads to significant alterations in many organ systems, with the kidney being particularly susceptible to age-related changes. Within the kidney, aging leads to ultrastructural changes such as glomerular and tubular hypertrophy, glomerulosclerosis, and tubulointerstitial fibrosis, which may compromise renal plasma flow (RPF) and glomerular filtration rate (GFR). These alterations may reduce the functional reserve of the kidneys, making them more susceptible to pathological events when challenged or stressed, such as following exposure to nephrotoxicants. An important and prevalent environmental toxicant that induces nephrotoxic effects is mercury (Hg). Since exposure of normal kidneys to mercuric ions might induce glomerular and tubular injury, aged kidneys, which may not be functioning at full capacity, may be more sensitive to the effects of Hg than normal kidneys. Age-related renal changes and the effects of Hg in the kidney have been characterized separately. However, little is known regarding the influence of nephrotoxicants, such as Hg, on aged kidneys. The purpose of this review was to summarize known findings related to exposure of aged and diseased kidneys to the environmentally relevant nephrotoxicant Hg.

Mechanisms involved in the transport of mercuric ions in target tissues.

Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.

Compensatory Renal Hypertrophy and the Uptake of Cysteine S-Conjugates of Hg2+ in Isolated S2 Proximal Tubular Segments.

Chronic kidney disease is characterized by a progressive and permanent loss of functioning nephrons. In order to compensate for this loss, the remaining functional nephrons undergo significant structural and functional changes. We hypothesize that luminal uptake of inorganic mercury (Hg2+), as a conjugate of cysteine (Cys; Cys-S-Hg-S-Cys), is enhanced in S2 segments of proximal tubules from the remnant kidney of uninephrectomized (NPX) rabbits. To test this hypothesis, we measured uptake and accumulation of Cys-S-Hg-S-Cys in isolated perfused S2 segments of proximal tubules from normal (control) and NPX rabbits. The remnant kidney in NPX rabbits undergoes significant hypertrophy during the initial 3 weeks following surgery. Tubules isolated from NPX rabbits were significantly larger in diameter and volume than those from control rabbits. Moreover, real-time PCR analyses of proximal tubules indicated that the expression of selected membrane transporters was greater in kidneys of NPX animals than in kidneys of control animals. When S2 segments from control and NPX rabbits were perfused with cystine or Cys-S-Hg-S-Cys, we found that the rates of luminal disappearance and tubular accumulation of Hg2+ were greater in tubules from NPX animals. These increases were inhibited by the addition of various amino acids to the perfusate. Taken together, our data suggest that hypertrophic changes in proximal tubules lead to an enhanced ability of these tubules to take up and accumulate Hg2.

Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg-Carbon Bond Cleavage and Metal Binding Specificity.

In bacterial resistance to mercury, the organomercurial lyase (MerB) plays a key role in the detoxification pathway through its ability to cleave Hg-carbon bonds. Two cysteines (C96 and C159; Escherichia coli MerB numbering) and an aspartic acid (D99) have been identified as the key catalytic residues, and these three residues are conserved in all but four known MerB variants, where the aspartic acid is replaced with a serine. To understand the role of the active site serine, we characterized the structure and metal binding properties of an E. coli MerB mutant with a serine substituted for D99 (MerB D99S) as well as one of the native MerB variants containing a serine residue in the active site (Bacillus megaterium MerB2). Surprisingly, the MerB D99S protein copurified with a bound metal that was determined to be Cu(II) from UV-vis absorption, inductively coupled plasma mass spectrometry, nuclear magnetic resonance, and electron paramagnetic resonance studies. X-ray structural studies revealed that the Cu(II) is bound to the active site cysteine residues of MerB D99S, but that it is displaced following the addition of either an organomercurial substrate or an ionic mercury product. In contrast, the B. megaterium MerB2 protein does not copurify with copper, but the structure of the B. megaterium MerB2-Hg complex is highly similar to the structure of the MerB D99S-Hg complexes. These results demonstrate that the active site aspartic acid is crucial for both the enzymatic activity and metal binding specificity of MerB proteins and suggest a possible functional relationship between MerB and its only known structural homologue, the copper-binding protein NosL.

Accumulation properties of inorganic mercury and organic mercury in the red-crowned crane Grus japonensis in east Hokkaido, Japan.

The red-crowned (Japanese) crane Grus japonensis is native to east Hokkaido, Japan, in contrast to the East Asia mainland. Previously, we reported that red-crowned cranes in Hokkaido were highly contaminated with mercury in the 1990s and that the contamination rapidly decreased to a moderate level in the 2000s. In the present study, we determined levels of organic mercury (O-Hg) in the liver and kidney of cranes in east Hokkaido in comparison with levels of total mercury (T-Hg). T-Hg levels in the kidneys were higher than those in the livers in adults but not in subadults and juveniles; however, the reverse was the case for O-Hg even for adults. The ratio of O-Hg to T-Hg in both the liver and kidney decreased as T-Hg increased in the three developmental stages. While the ratios of O-Hg to T-Hg in the liver and kidney of adults were significantly lower than those of juveniles, the ratios were similar for adults and juveniles in a lower range of T-Hg. The ratio of selenium (Se) to T-Hg decreased as T-Hg increased in both the liver and kidney, irrespective of stages. Mercury burdens in feathers were about 59% and 67% of the total body burdens for juveniles and adults, respectively. Furthermore, ratios of carbon and nitrogen stable isotopes to T-Hg varied greatly, with no relation to mercury level in the liver. The results suggest slow accumulation of inorganic mercury in the kidney of red-crowned cranes in east Hokkaido, Japan.

Organic and inorganic mercurials have distinct effects on cellular thiols, metal homeostasis, and Fe-binding proteins in Escherichia coli.

The protean chemical properties of the toxic metal mercury (Hg) have made it attractive in diverse applications since antiquity. However, growing public concern has led to an international agreement to decrease its impact on health and the environment. During a recent proteomics study of acute Hg exposure in E. coli, we also examined the effects of inorganic and organic Hg compounds on thiol and metal homeostases. On brief exposure, lower concentrations of divalent inorganic mercury Hg(II) blocked bulk cellular thiols and protein-associated thiols more completely than higher concentrations of monovalent organomercurials, phenylmercuric acetate (PMA) and merthiolate (MT). Cells bound Hg(II) and PMA in excess of their available thiol ligands; X-ray absorption spectroscopy indicated nitrogens as likely additional ligands. The mercurials released protein-bound iron (Fe) more effectively than common organic oxidants and all disturbed the Na(+)/K(+) electrolyte balance, but none provoked efflux of six essential transition metals including Fe. PMA and MT made stable cysteine monothiol adducts in many Fe-binding proteins, but stable Hg(II) adducts were only seen in CysXxx(n)Cys peptides. We conclude that on acute exposure: (a) the distinct effects of mercurials on thiol and Fe homeostases reflected their different uptake and valences; (b) their similar effects on essential metal and electrolyte homeostases reflected the energy dependence of these processes; and (c) peptide phenylmercury-adducts were more stable or detectable in mass spectrometry than Hg(II)-adducts. These first in vivo observations in a well-defined model organism reveal differences upon acute exposure to inorganic and organic mercurials that may underlie their distinct toxicology.