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At least 19 recordsLinked to original sources
PubMed1979

Arsenite inhibits beta-oxidation in isolated rat liver mitochondria.

A partial inhibition of acylcarnitine oxidation by arsenite in rat liver mitochondria has been studied. This inhibition is confined to the thiolase(s). The inhibition was observed also in the presence of malate, indicating no selective effect on ketogenesis. Ketogenesis from acetyl-CoA was inhibited by arsenite. Mitochondrial CoA was acylated by acylcarnitine nearly as rapidly in the presence of arsenite as in its absence. Thus, arsenite did not interfere with the availibility of CoA in the mitochondria. No effect of arsenite on enzymes of beta-oxidation other than the thiolase(s) was observed. When arsenite and acylcarnitine were added simultaneously to mitochondria, there was a delay before maximal inhibition of oxygen uptake occurred. When the mitochondria were preincubated with arsenite before addition of acylcarnitine, the inhibitory effect on oxygen utilization was initially large, but then partially repealed. Similar time delays were observed in the activity of acetoacetyl-CoA thiolase of disrupted mitochondria depending on the sequence of arsenite and acetoacetyl-CoA addition. It is suggested that substrate and arsenite complete for the reactive sulfhydryl group at the active site of the thiolase(s).

Acetyl-CoA C-Acetyltransferase↗
PubMed1977

Effects of arsenite on DNA repair in Escherichia coli.

Since environmental exposure to arsenicals has been correlated with a high skin cancer risk among populations exposed to sunlight, it is possible that arsenicals might interfere with the repair of damage to DNA (mostly thymine dimers) resulting from the ultraviolet rays in sunlight. To test this hypothesis, strains of E. coli, differing from each other only in one or more repair functions, were exposed to UV light and then plated in the presence or absence of sodium arsenite. Survival after irradiation of wild type E. coli (WP(2)) was significantly decreased by 0.5mM arsenite. This effect was also seen in strains which are unable to carry out excision repair, suggesting that arsenite inhibits one or more steps in the post-replication repair pathways. This is confirmed by the finding that arsenite has no effect on the post-irradiation survival of a recA mutant, which does not carry out post-replication repair. Mutagenesis after ultraviolet irradiation depends on the rec(+) and lex(+) genes. Arsenite decreases mutagenesis in strains containing these genes. In order to determine its mechanism of action, dose-response relationships of arsenite on a number of cellular functions were carried out. The most sensitive cellular functions found were the induction of beta-galactosidase and the synthesis of RNA. Since error-prone repair in E. coli is an inducible process, the inhibition of mutagenesis after UV irradiation may be the result of inhibition of messenger RNA synthesis.

Animals↗
PubMed1979

Effect of arsenite on renal tissue slice metabolism in chronic metabolic acidosis and alkalosis.

Tissue slices prepared from renal cortex of littermate dogs with chronic metabolic acidosis or alkalosis were incubated in media with or without arsenite and containing 1 mM L-[14C]glutamine or [1,5-14C]citrate. The presence of arsenite increased the concentration of alpha-ketoglutarate in slices by 5--20 times the values found without this inhibitor. alpha-Ketoglutarate concentrations in acidotic slices were 40% or more greater than those in alkalotic ones when arsenited was present. 14C incorporation into alpha-ketoglutarate was also increased manyfold by arsenite with either labeled glutamine or citrate as substrate. 14CO2 production from labeled glutamine by over 90% and from labeled citrate by over 75%; the difference between 14CO2 production by acidotic and alkalotic slices was greatly reduced or eliminated by arsenite. These results suggest that in chronic metabolic acidosis metabolism of both glutamine and citrate is stimulated at a site or sites preceding formation of alpha-ketoglutarate.

Acidosis↗
PubMed1977

Effects of quaternary ligands on the inhibition of acetylcholinesterase by arsenite.

Arsenite inhibits acetylcholinesterase in a second-order reaction. The rate and equilibrium constants depend upon pH and have values on the order of 10(2) M-1 min-1 and 10(5) M (dissociation), respectively. Some quaternary ammonium ligands completely block the arsenite inhibition of the enzyme, others decrease the rate of the reaction and some, notably pyridine-2 aldoxime methiodide, greatly accelerate the rate of the reaction, up to 220-fold. Accelerators may bind at a separate enzyme site distinct form the anionic site involved in substrate binding. Although the kinetic data are consistent with a covalent reaction between arsenite and acetylcholinesterase, chemical evidence excludes the involvement of sulfhydryl groups which are usually implicated in arsenite inhibition.

Ammonia↗
PubMed1975

The oxidation of arsenite in seawater.

The oxidation rate of arsenite in seawater is very slow. Of the parameters investigated which might affect this rate the most important were temperature, initial arsenite concentration, salinity and pH. An empirical rate expression was developed from experimental data which led to a prediction that the natural rate of oxidation in the ocean is about 0.023 micromoles of As(III) per liter each year. This value is about twice the natural concentration of arsenite; the only mechanism which seems able to account for the continued presence of arsenite is biological reduction of arsenate.

Arsenic↗
PubMed1978

The interaction of arsenite with the molybdenum center of chicken liver xanthine dehydrogenase.

Inactivation of chicken liver xanthine dehydrogenase by arsenite is reflected in the molybdenum electron paramagnetic resonance signal at g = 1.97. The arsenite spectrum shows additional splittings and considerable broadening yet remains comparable to the native in total intensity. Further subtle alterations of the molybdenum signal of arsenite-treated enzyme are seen in the presence of purine-type substrates or inhibitors.

Animals↗
PubMed1978

Arsenic and cancer: effects of joint administration of arsenite and selenite on the genesis of mammary adenocarcinoma in inbred female C3H/St mice.

The joint administration of 2 ppm of arsenic as arsenite and of 2 ppm of selenium as selenite in the drinking water of inbred female C3H/St mice increases the incidence of spontaneous mammary adenocarcinoma significantly over the simultaneous controls and animals receiving 2 ppm As as arsenite or 2 ppm Se as selenite alone, indicating that arsenic abolishes the anticarcinogenic effect of selenium. Arsenite caused a significant increase of the tumor growth rates and raised the incidence of multiple tumors. The tumor growth rates in the As-Se group were also increased, but the incidence of multiple tumors was lower than in the 2 ppm As group.

Adenocarcinoma↗
PubMed1977

Energy-dependent uptake of arsenite by rat liver mitochondria.

Uptake of arsenite by rat liver mitochondria is energy-dependent, as shown by comparing values without and with either uncoupling agent or respiratory inhibitor present. The uptake is inhibited by mersalyl and N-ethylmaleimide, which can be used as 'stopping' agents to obtain uptake kinetics. At 20 degrees C the process is nearly complete in 1 min. The relation between the quantity in the energized mitochondria and the applied concentration corresponds to at least two different modes of binding of the arsenite. Competition occurs between arsenite and other anions (for example, phosphate) for intramitochondrial accumulation.

Animals↗
PubMed1976

Oxidation of arsenite to arsenate by Alcaligenes faecalis.

Alcaligenes faecalis, resistant to the toxic effects of 0.01 M sodium arsenite, was isolated from raw sewage and shown to be capable of oxidizing arsenite to arsenate. When the organisms were grown in chemically defined medium, this conversion was due to the appearance at stationary phase of an intracellular, oxygen-sensitive, inducible enzyme and/or component of the electron transport system; when the organisms were grown in a nutrient broth-yeast extract medium, the enzyme appeared in the late exponential phase of growth. The presence of 0.02 M arsenite in the culture medium affected neither growth rate nor final cell yield.

2,6-Dichloroindophenol↗
PubMed1976

Effect of sodium arsenite on the biosynthesis of mitomycins by Streptomyces caespitosus and mode of action of mitomycin C on Bacillus subtilis NRRL B-543.

Addition of different concentrations of sodium arsenite to the fermentation medium used for the production of mitomycin antibiotics by Streptomyces caespitosus hindered the biosynthesis of mitomycins and led to the accumulation of 2-oxoglutarate, pyruvate and acetone. Mitomycin C isolated and purified using thin-layer chromatography in low concentration of about 0.1 mug/ml did not affect the RNA, DNA and protein biosynthesis of the growing Bacillus subtilis, while at 10 mug/ml mitomycin C markedly affected RNA, DNA and protein biosynthesis.

Acetone↗
PubMed1978

Effects of thiol inhibitors on hepatic guanylate cylase activity.

Several thiol blocking agents inhibit basal guanylate cyclase activity of 100 000 X g hepatic supernatant fractions and the stimulation of enzyme activity by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), NaN3, NaNO2 and nitroprusside. The relative potency of the thiol blockers as inhibitors was CdCl2 greater than p-hydroxymercuribenzoate greater than N-ethylmaleimide greater than arsenite greater than iodoacetamide. Inhibition of basal and MNNG-responsive soluble guanylate cyclase activities by arsenite was markedly potentiated by an equimolar concentration of 2,3-dimercaprol, but not by mercaptoethanol. Inhibition of soluble guanylate cyclase by either arsenite or CdCl2 was completely reversed by excess 2,3-dimercaprol. Qualitatively similar effects were observed with DE-52 cellulose purified soluble hepatic guanylate cyclase, and suggested an involvement of closely juxtaposed thiol groups in the regulation of enzyme activity. For several reasons inhibition by thiol blockers appeared to be mediated through multiple mechanisms and/or sites of interaction: (1) Concentrations of the thiol inhibitors which had no effect on basal activity strikingly inhibited the responsiveness of the enzyme to a submaximal concentration of MNNG. (2) CdCl2 abolished the action of excess MnCl2 to stimulate purified guanylate cyclase, but was a relatively ineffective inhibitor when MnCl2 and GTP were present in equimolar concentrations. By contrast, arsenite-2,3-dimercaprol was uniformly effective in inhibiting guanylate cyclase activity in the presence or absence of excess MnCl2. (3) Arsenite-2,3-dimercaprol increased the Km for MnGTP (control, 0.13 +/- 0.02 mM; 0.2 mM arsenite-2,3-dimercaprol, 0.31 +/- 0.03 mM), whereas CdCl2 had no effect on this parameter. (4) Hepatic particulate guanylate cyclase activity was significantly inhibited by arsenite 2,3-dimercaprol but not by CdCl2. Thus, the data not only indicate that vicinal dithiol groups are required for expression of basal guanylate cyclase activity and enzyme responses to agonists, but strongly suggest the involvement of more than one interacting site containing free thiol residues.

Animals↗
PubMed1977

Inorganic salts resistance associated with a lactose-fermenting plasmid in Streptococcus lactis.

Present evidence indicates that lactose metabolism in group N streptococci is linked to plasmid deoxyribonucleic acid. Lactose-positive (Lac+) Streptococcus lactis and lactose-negative (Lac-) derivatives were examined for their resistance to various inorganic ions. Lac+ S. lactis strains ML3, M18, and C2 were found more resistant to arsenate (7.5- to 60.2-fold), arsenite (2.25- to 3.0-fold), and chromate (6.6- to 9.4-fold), but more sensitive to copper (10.0- to 13.3-fold) than their Lac- derivatives. These results suggested that genetic information for resistance and/or sensitivity to these ions resides on the "lactose plasmid." Kinetics of ultraviolet irradiation inactivation of transducing ability for lactose metabolism and arsenate resistance confirmed the plasmid location of the two markers. Lac+ transductants from S. lactis C2 received genetic determinants for resistance to arsenate, arsenite, and chromate but not for copper sensitivity. In this case, resistance markers were lost when the transductants became Lac- but the derivatives remained copper resistant. The resistant markers for arsenate and arsenite could not be identified as separate genetic loci, but chromate resistance and copper sensitivity markers were found to be independent genetic loci. The "lactose plasmid" from S. lactis C10 possessed the genetic loci for arsenate and arsenite resistance but not for chromate resistance or copper sensitivity.

Arsenates↗