High Potassium Ion Concentration Research Articles

EFEITO DA CONCENTRAÇÃO DE POTÁSSIO NA EFICIÊNCIA DO EXTRATO DE SEMENTES DE MORINGA COMO AGENTE COAGULANTE

Estudos indicam que sais potencializam o efeito coagulante do extrato de sementes de moringa (Moringa oleifera), tendo sido obtidos resultados satisfatórios quando preparado em solução de cloreto de sódio e hidróxido de cálcio. Entretanto, a presença de íons monovalentes em águas residuárias pode favorecer a dispersão dos sólidos, impedindo a formação de flocos e a sedimentação dos sólidos, reduzindo a eficiência de redução na turbidez. Sabe-se que o efluente de filtros orgânicos, gerado, por exemplo, quando se utiliza serragem de madeira como material filtrante, e águas residuárias como as do processamento do fruto do cafeeiro e vinhaça, apresentam altas concentrações do íon monovalente potássio. No presente trabalho, objetivou-se avaliar a eficiência do extrato de sementes de moringa, como agente coagulante, na remoção de turbidez de água (turbidez de 106 UNT) com concentrações de potássio de 0 a 375 mg L-1. Verificou-se que o potássio, quando presente em concentrações de até 2 mg L-1, proporcionou efeito dispersivo no material sólido em suspensão, entretanto, a partir daí, crescente eficiência na coagulação dos sólidos presentes e, consequentemente, redução na turbidez da água.

Potassium ion-dependent trehalose phosphorylase from halophilic Bacillus selenitireducens MLS10

We discovered a potassium ion-dependent trehalose phosphorylase (Bsel_1207) belonging to glycoside hydrolase family 65 from halophilic Bacillus selenitireducens MLS10. Under high potassium ion concentrations, the recombinant Bsel_1207 produced in Escherichia coli existed as an active dimeric form that catalyzed the reversible phosphorolysis of trehalose in a typical sequential bi bi mechanism releasing β-d-glucose 1-phosphate and d-glucose. Decreasing potassium ion concentrations significantly reduced thermal and pH stabilities, leading to formation of inactive monomeric Bsel_1207.

New Technologies for Decontamination of Radioactive Substances Scattered by Nuclear Accident / Nowe Technologie Dekontaminacji Radioaktywnych Substancji Rozproszonych Przez Awarie Nuklearna

Our effort for decontamination of radioactive cesium scattered widely by nuclear accident in March 2011 in Fukushima, Japan has been described. Radioactive cesium scattered widely in Japan has been accumulating in arc or plasma molten-solidified ash in waste incinerating facilities up to 90,000 Bq/kg of the radioactive waste. Water rinsing of the ash resulted in dissolution of cesium ions together with high concentrations of potassium and sodium ions. Although potassium inhibits the adsorption of cesium on zeolite, we succeeded to precipitate cesium by in-situ formation of ferric ferrocyanide and iron rust in the radioactive filtrate after rinsing of the radioactive ash with water. Because the regulation of no preservation of any kind of cyanide substances, cesium was separated from the precipitate consisting of cesium-captured ferric ferrocyanide and ferric hydroxide in diluted NaOH solution and subsequent filtration gave rise to the potassium-free radioactive filtrate. Cesium was captured by zeolite from the potassium-free radioactive filtrate. The amount of this final radioactive waste of zeolite was significantly lower than that of the arc-molten-solidified ash.

Suppressions of spiral waves and spatiotemporal chaos in cardiac tissue

Suppressions of spiral waves and spatiotemporal chaos in cardiac tissue are investigated by using the Luo-Rudy phase I model. Two control methods are proposed. (Ⅰ) A planar wave is generated by alternately changing the extracellular potassium ion concentration, and then a weak external electric field is used to help plane wave to suppress spiral waves and spatiotemporal chaos. (Ⅱ) The extracellular potassium ion concentration is first enhanced. Planar waves are then generated by the wave emission induced by an external electric field. We use the planar waves to suppress the spiral waves and spatiotemporal chaos. The results show that the control methods can effectively suppress spiral waves and spatiotemporal chaos when relevant parameters are appropriately chosen. When regional myocardial ischemia occurs, high extracellular potassium ion concentration will appear where myocardial ischemia occurs. The methods of wave emission can be used to suppress spiral waves and spatiotemporal chaos in heart in this case. The advantages and mechanism of the control methods are explained.

Dengue Virus Capsid Protein Binding to Hepatic Lipid Droplets (LD) Is Potassium Ion Dependent and Is Mediated by LD Surface Proteins

Dengue virus (DENV) affects millions of people, causing more than 20,000 deaths annually. No effective treatment for the disease caused by DENV infection is currently available, partially due to the lack of knowledge on the basic aspects of the viral life cycle, including the molecular basis of the interaction between viral components and cellular compartments. Here, we characterized the properties of the interaction between the DENV capsid (C) protein and hepatic lipid droplets (LDs), which was recently shown to be essential for the virus replication cycle. Zeta potential analysis revealed a negative surface charge of LDs, with an average surface charge of -19 mV. The titration of LDs with C protein led to an increase of the surface charge, which reached a plateau at +13.7 mV, suggesting that the viral protein-LD interaction exposes the protein cationic surface to the aqueous environment. Atomic force microscopy (AFM)-based force spectroscopy measurements were performed by using C protein-functionalized AFM tips. The C protein-LD interaction was found to be strong, with a single (un)binding force of 33.6 pN. This binding was dependent on high intracellular concentrations of potassium ions but not sodium. The inhibition of Na(+)/K(+)-ATPase in DENV-infected cells resulted in the dissociation of C protein from LDs and a 50-fold inhibition of infectious virus production but not of RNA replication, indicating a biological relevance for the potassium-dependent interaction. Limited proteolysis of the LD surface impaired the C protein-LD interaction, and force measurements in the presence of specific antibodies indicated that perilipin 3 (TIP47) is the major DENV C protein ligand on the surface of LDs.

Early Fetal Development of the Human Cochlea

The cochlear scalas are differentiated from a single tube with a lining by the tall epithelium, that is, the cochlear duct. However, we have no information about the mechanism involved in the formation of the scalas. We evaluated histological sections taken from 20 fetuses: eight each at 8--9 weeks [early stage; 28--45 mm crown-rump length (CRL)] and 11--12 weeks (middle stage; 52--74 mm CRL), and four at 14--15 weeks (late stage; 90--110 mm CRL) of gestation. In four of eight early-stage and in all eight middle-stage specimens, we observed irregular perilymphatic spaces and their fusion; these spaces tended to be larger in the future scala tympani than in the future scala vestibuli. The cochlear duct epithelium was positive for cytokeratin 19 in contrast to the other parts of the cochlea. The tectorial membrane appeared in two of eight middle-stage and all four late-stage specimens. After 16 weeks, mesothelial lining of the scala may follow the development of aquaporin-positive thin blood vessels along the scala wall. Notably, gap formation of the cochlear duct epithelium at a site facing the scala tympani consistently occurred before the development of S100 protein-negative organ of Corti. This gap is likely to correspond to a site occupied finally by Hensen's cells. All these steps likely started in the basal coil and extended to the apical side of the cochlea. These findings suggest that leakage through the epithelial gap of endolymph, with a high concentration of potassium ions, causes mesenchymal cell death, leading to the coalescence of vacuoles containing low potassium perilymph.

Use of cultured human neuroblastoma cells in rapid discovery of the voltage-gated potassium-channel blockers.

Depolarization of human neuroblastoma cells by high concentrations of extracellular potassium ions, leads to the activation of the voltage-gated potassium channels. The activity of such potassium channels can be effectively and rapidly monitored by tracking the efflux of 86Rb from pre-loaded target cells in response to the depolarizing stimulus. The inclusion of compounds with unknown activity in the assay medium, can result in the identification of novel blockers of the voltage-gated potassium channels. Since this functional assay is performed in 96-well microtitre plates, it represents a rapid and high-volume primary screening method for the detection and identification of the voltage-gated potassium-channel blockers, which may have therapeutic utility in several indications including memory degeneration and cardiac arrhythmias.

Similarities in functional attributes and nutritional effects of magadi soda and bean debris-ash used in cooking African traditional dishes

Magadi soda and bean debris-ash have been used as condiments for a long time by various ethnic groups in East and Central Africa in cooking traditional dishes. The aim of the study was to investigate whether magadi soda and bean debris-ash had similar effects and functional attributes when added to traditional dishes during cooking. Reason for the addition of the two condiments has not been revealed by researchers. Mineral content, in-vitro bioavailability studies and pH of non-ashed and ashed magadi soda and bean debris were evaluated. The results indicated that high concentrations of sodium ions (30.2%) and potassium ions (64.2%) were observed in magadi soda and bean debris-ash, respectively. In-vitro iron and zinc bioavailability decreased significantly with the addition of magadi soda and bean debris-ash in maize, beans and sorghum. Equally, the cooking time was significantly reduced. The mean pH for both magadi soda (9.66) and bean debris-ash (9.75) were not significantly different indicating that both aqueous solutions had alkaline properties. The similarity in properties especially in mineral profile, alkalinity, decreased cooking time and lowered mineral uptake by magadi soda and bean debris-ash explain similar functionality in foods they are added to during cooking. Despite the similarities observed, communities should be informed of the negative nutritional effects of these condiments so as to diversify their meal patterns accordingly. Key words : Magadi soda, bean ash, traditional dishes, minerals, in-vitro bioavailability

Bronchorelaxant property of African potato' (Hypoxis hemerocallidea corm) aqueous extract in vitro

This study was undertaken to investigate the bronchorelaxant effect of Hypoxis hemerocallidea corm ('African potato') aqueous extract (APE) on spasmogen-provoked contractions of guinea-pig isolated tracheal smooth muscle preparations. APE (25-400 mg/ml) relaxed spasmogen (histamine-, carbachol- and potassium-)-induced contractions of the isolated tracheal muscle preparations in a concentration-dependent manner. The relaxant effects of APE on spasmogen-evoked contractions of the tracheal muscle preparations were not altered by bath-applied propranolol (0.1-5.0 microg/ml), which markedly inhibited or completely abolished the relaxant effects of isoprenaline (0.1-5.0 microg/ml). Although the precise mechanism of the bronchorelaxant effect of APE could not be established in the present study, it is unlikely that the herb's aqueous extract stimulates the beta(2)-adrenoceptors present on the bronchial smooth muscles to produce its bronchodilatation. The finding that APE significantly relaxed (P<0.05) histamine-, carbachol- and high potassium ion concentration (K(+), 80 mM)-induced contractions of guinea-pig isolated bronchial muscle preparations appears to suggest that the bronchospasmolytic effect of the plant's extract is probably not mediated through a specific receptor, but rather, probably mediated via a non-specific bronchospasmolytic mechanism.

High extracellular potassium ion concentration attenuates the blockade action of ketanserin on Kv1.3 channels expressed in xenopus oocytes

Ketanserin (KT), a selective serotonin (5-HT) 2-receptor antagonist, reduces peripheral blood pressure by blocking the activation of peripheral 5-HT receptors. In this study electrophysiological method was used to investigate the effect of KT and potassium ion on Kv1.3 potassium channels and explore the role of blocker KT in the alteration of channel kinetics contributing to the potassium ion imbalances. Kv1.3 channels were expressed in xenopus oocytes, and currents were measured using the two-microelectrode voltage-clamp technique. KCl made a left shift of activation and an inactivation curve of Kv1.3 current and accelerated the activation and inactivation time constant. High extracellular [K(+)] attenuated the blockade effect of KT on Kv1.3 channels. In the presence of KT and KCl the activation and inactivation time constants were not influenced significantly no matter what was administered first. KT did not significantly inhibit Kv1.3 current induced by tetraethylammonium (TEA). KT is a weak blocker of Kv1.3 channels at different concentrations of extracellular potassium and binds to the intracellular side of the channel pore. The inhibitor KT of ion channels is not fully effective in clinical use because of high [K(+)](o) and other electrolyte disorders.

The effect of applying potassium chloride solutions at atmospheric pressure on the sensitivity of dentine in man

Objective To determine the effects of applying KCl solutions to exposed dentine at atmospheric pressure on pain evoked by probing and air blast stimuli in human subjects. Design The experiments were carried out on 24 premolars in 16 subjects (aged 16–30 years). A cavity (diameter 3 mm, depth 3 mm) was cut at the tip of the buccal cusp and etched with 35% orthophosphoric acid. The cavity was filled with 500, 250 mmol/l KCl or 500 mmol/l NaCl for 10 min, after which it was rinsed with normal saline. Each solution was tested in 8 teeth. Air blast and probing stimuli were applied to the exposed dentine prior to dentine treatment and at 0, 2, 5, 10, and 20 min after treatment. After each stimulus the subject indicated the intensity of the pain evoked on a visual analogue scale (VAS). Results In teeth treated with 250 or 500 mmol/l KCl, the mean VAS response to air blast stimuli was significantly decreased at 5 and 10 min after treatment. The mean VAS response to probing was significantly decreased 10 min after treatment with 500 mmol/l KCl. Otherwise there were no significant changes. Conclusion Topical application to exposed dentine of solutions containing a high concentration of potassium ions at atmospheric pressure produce a temporary reduction in the sensitivity of dentine to air blast and probing stimuli.

Concentrations of Nitrate, Organic Acids, Free Amino Acids, Cations and Sugars in Komatsuna (Brassica campestris var. perviridis) Grown with Carbonate, Sulfate and Chloride Application

This study compared the concentrations of components such as nitrate, organic acids, free amino acids, cations and sugars in komatsuna (Brassica campestris var. perviridis) grown with carbonate, sulfate and chloride application (CO3-TK, SO4-TK and Cl-TK, respectively). The komatsuna was cultivated in 1/2000-a Wagner pots (6 hills per pot) filled with light-colored Andosol in a glasshouse for 37 days at soil water potential (SWP) right before harvesting of −6.2 and −62 kPa. And 26.5 mmolc of carbonate, sulfate or chloride in the form of potassium salts was applied to each pot. Chloride application to the komatsuna induced relatively high concentrations of potassium, calcium and magnesium ions, and the low concentrations of malate, glucose and fructose on a dry weight basis (DWB). Carbonate application induced relatively high concentrations of malate and low concentrations of nitrate. Sulfate was almost between chloride and carbonate. Concentration variation was not substantial in free amino acids. Those tendencies were almost the same in both SWPs. Most of the variations in component concentrations were attributed to the regulation of ionic and osmotic balance to respond to chloride, nitrate and sulfate absorption, as judged from quantitative relationships among the components and water in the komatsuna. It seems that the absorption of nitrate is influenced by the pH of the soil. There were clear differences in glucose, fructose and malate concentrations among CO3-TK, SO4-TK and Cl-TK on a fresh weight basis just as on a DWB.

Pyrene Excimer Fluorescence as a Probe for Parallel G-Quadruplex Formation

The formation and properties of G-quadruplex structures from short single-strand oligonucleotide conjugates possessing two to four guanines and a 5'-terminal pyrenebutanol are reported. The 4-G conjugate forms a stable G-quadruplex under low or high potassium ion concentrations, whereas the 3-G conjugate forms a stable G-quadruplex only in the presence of high potassium. The 2-G conjugate fails to form a stable G-quadruplex even at low temperature and high potassium concentration. Both pyrene monomer and excimer fluorescence are observed for the G-quadruplex structures, whereas only monomer fluorescence is observed for the single-strand conjugates. Thus, pyrene excimer fluorescence can be used as a probe for the formation of G-quadruplex structures. The excimer/monomer intensity ratios for the G-quadruplex structures are dependent upon both the temperature and potassium or lithium salt concentration. The salt effect is attributed to a change in the structure of the hydrophobic pyrene chromophores, which are assembled on the 5'-face of the G-quadruplex as a consequence of electrostriction.

Mechanical and electrical responses modulated by excitation of inhibitory nerves during stimulation with high-potassium solutions in circular smooth muscle of the rabbit rectum

The properties of the mechanical responses produced by solutions containing high concentrations of potassium ion (high-K solution, [K(+)](o) = 9-27 mM) were investigated in circular smooth muscle preparations isolated from the rabbit rectum. Isometric recording of mechanical responses of the muscle revealed spontaneous contractions, which successively decreased and finally disappeared in most preparations. Stimulation of the smooth muscle with high-K solutions elicited an increase in both amplitude and frequency of twitch contractions (sustained component), with about a 2 min delay in the beginning (initial inhibition), and a transient large contraction shortly after the cessation of stimulation (after contraction). Transmural nerve stimulation (TNS) with electrical pulses for 1 min at 1 Hz frequency produced a sustained inhibition, but a transient contraction followed after termination of TNS. In the presence of tetrodotoxin (TTX), the TNS-induced responses were abolished, while a high-K solution elicited increased twitch contractions with a short delay and abolished the after contraction. Suramin produced effects similar to TTX on the responses produced by high-K solutions or TNS, but this was not the case for atropine, guanethidine or N(omega)-nitro-L-arginine (L-NA). Recording membrane potentials with microelectrodes revealed that TNS evoked an inhibitory junction potential (i.j.p.) which was non-adrenergic, non-cholinergic and non-nitrergic in nature. High-K solutions elicited a tri-phasic change in the membrane potential; an initial hyperpolarization, followed by a sustained depolarization and finally a transient depolarization on cessation of high-K stimulation. TTX or suramin inhibited the i.j.p.s and altered the tri-phasic change in the membrane potential produced by a high-K solution to a mono-phasic depolarization. No significant modulation of electrical responses of the membrane induced by TNS or high-K solution was elicited by atropine, guanethidine or L-NA. The results indicated that the circular smooth muscle of the rabbit rectum is innervated by inhibitory nerves, and that stimulation with high-K solutions caused inhibitory neuronal modulation of both electrical and mechanical responses of the smooth muscle, in a suramin-sensitive way.

Molecular Identification and Functional Characterization of Rat Multidrug and Toxin Extrusion Type Transporter 1 as an Organic Cation/H+Antiporter in the Kidney

We have cloned and functionally characterized the rat ortholog of multidrug and toxin extrusion type transporter 1 (rMATE1). The mRNA of rMATE1 was strongly expressed in kidney and detectable in the various tissues such as brain, stomach, colon, lung, liver, spleen, skeletal muscle, and prostate. When stably expressed in HEK293 cells, rMATE1 could mediate the transport of tetraethylammonium (TEA) and cimetidine under the condition where the membrane potential was disrupted by a high concentration of potassium ion and intracellular pH was reduced by NH(4)Cl pretreatment. When extracellular pH was changed from 5.5 to 8.5, the transport of TEA by rMATE1 was greatest at pH 7.5. Kinetic analyses showed that the transports of TEA and cimetidine mediated by rMATE1 were both saturable with a K(m) of 260 +/- 10 and 3.01 +/- 0.21 muM, respectively. It was found that cimetidine is the most potent inhibitor of rMATE1, and many other organic cations, such as 1-methyl-4-phenylpyridinium, amiloride, imipramine, and quinidine, are also effective as inhibitors. Pretreatment of the cells expressing rMATE1 with p-chloromercuribenzene sulfonate significantly reduced TEA transport, but this effect was totally reversed by subsequent treatment with dithiothreitol. These results indicate that the functional nature of rMATE1 is consistent with that of the hypothetical organic cation/H(+) antiporter system in the brush-border membrane of the renal tubular epithelial cells. Accordingly, these results suggest that rMATE1 is an electroneutral and multispecific organic cation transporter energized by the trans-proton gradient, and plays a physiological role in renal secretion of organic cations, including clinically used cationic drugs.

Chronic antidepressant treatment modulates the release of somatostatin in the rat nucleus accumbens

This study investigated the in vivo neuronal release of somatostatin in the rat nucleus accumbens (NAc), and the effect of chronic administration of antidepressants. Microdialysis studies were performed on male Sprague–Dawley rats, in accordance with the EU guidelines (EEC Council 86/609). Somatostatin levels were quantified by radioimmunoassay (RIA) or enzyme linked immuno sorbent assay (ELISA). A high concentration of potassium ions (K +, 100 mM) was used to ascertain the neuronal release of somatostatin. Antidepressant treatments involved the administration of citalopram (20 mg/2 ml/kg, i.p., once daily) or desipramine (DMI, 5 mg/2 ml/kg, i.p., twice daily) for 21 days. Control groups received saline (2 ml/kg for 21 days, i.p.) once or twice daily respective of the antidepressant treatment. Basal levels of somatostatin released were found to be 20.01 ± 0.52 fmol/sample. K + (100 mM) increased somatostatin levels at 205% of basal. Chronic citalopram and desipramine treatments also increased the somatostatin levels by 83 ± 32% and 40 ± 6% of basal, respectively. These findings indicate that somatostatin is released neuronally in the NAc. Antidepressants influence its release in a positive manner, suggesting the necessity of further studies for the elucidation of the involvement of somatostatin in the putative therapeutic effects of these agents.

Electrochemical Telomerase Assay with Ferrocenylnaphthalene Diimide as a Tetraplex DNA-Specific Binder

Spectroscopic studies revealed that ferrocenylnaphthalene diimide (1) can bind to tetraplex DNA at high potassium ion concentration. The tetraplex DNA was stabilized by the binding of 1, and this effect was larger than that of any other tetraplex stabilizers, which are known as a telomerase inhibitor. Quantitative analysis with circular dichroism and a quartz crystal microbalance strongly suggested a 3:1 binding stoichiometry of 1 to the tetraplex DNA. The telomere sequence could be extended by telomerase with the telomerase substrate primer on the surface of an electrode as proven by an increased current signal of 1 bound to the tetraplex DNA formed on the electrode. This is the first example of electrochemical detection of telomerase activity without relying on PCR.

Distribution of extracellular signal-regulated protein kinases 1 and 2 in the rat adrenal and their activation by angiotensin II

The adrenal gland of the rat is continuously regenerated through proliferation of a stem cell population in the outer part of the gland. To clarify the location of proliferative events within the adrenal gland, and the factors that stimulate them, rat adrenal capsule preparations, consisting of capsule, zona glomerulosa (ZG) and the outer zona fasciculata (ZF) were maintained in vitro under different conditions of stimulation, for varying periods. Sites of proliferation were identified by 5-bromo-2'-deoxy-uridine (BrdU) staining, and the distribution of classical MAP kinase (MAPK) family members, extracellular signal-regulated kinase (ERK) 1 and 2, immunoreactivity was determined using immunocytochemistry. BrdU staining was limited to the outer glomerulosa and the capsule, where it was enhanced by angiotensin II, but not by a high potassium ion concentration nor by ACTH. In contrast, ERK1/2 immunoreactivity was distributed throughout the ZG and in the medulla, with none detectable in the ZF and reticularis. Furthermore, angiotensin II, potassium ions and ACTH were all shown to induce ERK1 and ERK2 phosphorylation in the ZG. Treatment of adrenal capsule tissue with the specific MAPK kinase inhibitor PD98059 revealed inhibition of ERK1/2 phosphorylation, but no effect on angiotensin II-induced aldosterone secretion. Although the distribution and activation of the MAPK pathway suggest a link with proliferation, the findings clearly designated only the outer part of the glomerulosa and capsule as a potential stem cell population. Further functions should be sought for the apparently silent major part of the glomerulosa.

Observational and modeling analysis of a severe air pollution episode in western Hong Kong

A severe air pollution episode occurred over much of the western part of Hong Kong (HK) between 28 and 30 December 1999. In this study, multiple analyses were made to understand the cause of this episode; first, the main emission source of the pollution episode was identified using remote sensing techniques from satellite pictures and was located about 100 km to the northeast of HK. Second, analyses were made on PM10 chemical species characterization in four air quality monitor stations (AQMSs), and a high concentration of potassium ions (K+) on the episode days indicates the significant impact of biomass burning. The ratio of elemental carbon and organic carbon values in two western AQMSs indicated that regional transport, rather than the local vehicle emission and power plant, played an important role in this episode. This result is in contrast with the early finding by H. Liu and J. C. L. Chan that this pollution episode is solely due to local sources. Third, to study the transport, diffusion, and trapping of pollutants during this air pollution episode, two numerical models were coupled in this study: a three‐dimensional mesoscale meteorological model MM5 and a three‐dimensional Lagrangian particle dispersion model. With the help of the Lagrangian dispersion model we show that this severe air pollution event was associated with transport of pollutants over HK within the boundary layer. These pollutants were subsequently brought down to the surface by the local land‐sea breeze circulation and trapped over the western part of HK during the day by the same land‐sea breeze.

A recombinant exonuclease III homologue of the thermophilic archaeon Methanothermobacter thermautotrophicus

AP endonucleases catalyse an important step in the base excision repair (BER) pathway by incising the phosphodiester backbone of damaged DNA immediately 5′ to an abasic site. Here, we report the cloning and expression of the 774 bp Mth0212 gene from the thermophilic archaeon Methanothermobacter thermautotrophicus, which codes for a putative AP endonuclease. The 30.3 kDa protein shares 30% sequence identity with exonuclease III (ExoIII) of Escherichia coli and 40% sequence identity with the human AP endonuclease Ape1. The gene was amplified from a culture sample and cloned into an expression vector. Using an E. coli host, the thermophilic protein could be produced and purified. Characterization of the enzymatic activity revealed strong binding and Mg 2+-dependent nicking activity on undamaged double-stranded (ds) DNA at low ionic strength, even at temperatures below the optimum growth temperature of M. thermautotrophicus (65 °C). Additionally, a much faster nicking activity on AP site containing DNA was demonstrated. Unspecific incision of undamaged ds DNA was nearly inhibited at KCl concentration of ∼0.5 M, whereas incision at AP sites was still complete at such salt concentrations. Nicked DNA was further degraded at temperatures above 50 °C, probably by an exonucleolytic activity of the enzyme, which was also found on recessed 3′ ends of linearized ds DNA. The enzyme was active at temperatures up to 70 °C and, using circular dichroism spectroscopy, shown to denature at temperatures approaching 80 °C. Considering the high intracellular potassium ion concentration in M. thermautotrophicus, our results suggest that the characterized thermophilic enzyme acts as an AP endonuclease in vivo with similar activities as Ape1.