Effects Of Divalent Metal Cations Research Articles

Effect of Divalent Metal Cations on the Conformation, Elastic Behavior, and Controlled Release of a Photocrosslinked Protein Engineered Hydrogel.

We investigate the effect of Zn2+, Cu2+, and Ni2+ coordination on the conformation, mechanical properties, contraction, and small-molecule drug encapsulation and release of a photocrosslinked protein-engineered hydrogel, CEC-D. The treatment of the CEC-D hydrogel with divalent metal (M2+) results in significant conformational changes where a loss in structure is observed with Zn2+, while both Cu2+ and Ni2+ induce a blueshift. The relationship of M2+ to mechanical properties illustrates a trend, while the CEC-D hydrogel in the presence of 2 mM Cu2+ reveals the highest increase in G' to 14.4 ± 0.7 kPa followed by 9.7 ± 0.9 kPa by addition of 2 mM Zn2+, and a decrease to 1.1 ± 0.2 kPa is demonstrated in the presence of 2 mM Ni2+. A similar observation in M2+ responsiveness emerges where CEC-D hydrogels contract into a condensed state of 2.6-fold for Cu2+, 2.4-fold for Zn2+, and 1.6-fold for Ni2+. Furthermore, CEC-D hydrogels coordinated with M2+ demonstrate control over the encapsulation and release of the small molecule curcumin. The trend of release is opposite of the mechanical and contraction properties with a 70.0 ± 5.3% release with Ni2+, 64.2 ± 1.2% release with Zn2+, and 42.3 ± 11.3 release with Cu2+. Taken together, these results indicate that the CEC-D hydrogel tuned by M2+ is a promising drug delivery platform with tunable physicochemical properties.

Effect of micro‐aggregation behavior on the salt tolerance of polymer solutions

AbstractPolymer solution for oil displacement is mostly used in the middle and late stage of water flooding reservoir development, and reservoir groundwater conditions are often one of the main conditions restricting polymer application. Therefore, it is necessary to develop salt tolerance of polymer solutions with different aggregation behaviors, so as to facilitate the synthesis and optimization of suitable polymer systems. The differences in the micro‐aggregation behavior of three polymers with different molecular structures were explored. On this basis, the effects of divalent metal cations on the properties of the polymer solutions were analyzed by assessing the micro‐aggregation behavior, apparent viscosity, hydrodynamic size, and shear rheological characteristics. The results showed that the linear partially hydrolyzed polyacrylamide (HPAM) was seriously affected by divalent cations, and the viscosity decreased obviously. The aggregation behavior of the polymer changed by hydrophobic association can enhance the salt tolerance of the solution. The hydrophobically modified partially hydrolyzed polyacrylamide (HMPAM) with “chain beam” aggregation behavior has strong intermolecular connection, which enables it to withstand the content of calcium and magnesium ions of 1100 mg l−1. When the content of calcium and magnesium ions exceeds 600 mg l−1, dendritic hydrophobically associating polymer (DHAP) will destroy the interaction between molecular chains, resulting in the decrease of apparent viscosity and hydrodynamic size. For polymer flooding in high‐salinity reservoir, salt tolerant polymer system can be constructed by optimizing molecular weight and hydrophobic group content.

Effects of divalent metal cations and inorganic anions on the transport of tetracycline in saturated porous media: column experiments and numerical simulations.

Tetracycline is one of the most commonly used antibiotics in the world. Eventually, large amounts of this contaminant will enter into the subsurface environment, where a variety of ions exist. In this study, the effects of divalent metal cations (Mg2+, Ca2+, Pb2+ and Cu2+) and inorganic anions (Cl-, NO3-, SO42- and H2PO4-) on the transport of tetracycline in saturated porous media were investigated. Both batch and column experiments were conducted to determine the interactions between tetracycline and sand. Batch sorption experimental results showed that the presence of divalent metal cations could increase the sorption of tetracycline onto sand due to the cation-bridging mechanism. When Na+ was the counterion in the background solution, anions caused a significant decrease in tetracycline sorption owing to the occupation of some adsorption sites by anions and the decrease of electrostatic attraction. Column experiments indicated that the inhibition effects of divalent cations followed the order of Cu2+ > Pb2+ > Ca2+ ≈ Mg2+; the regular pattern might be related to their different complexing strengths. The presence of inorganic anions enhanced the mobility of tetracycline following the order of H2PO4- > SO42- > NO3- > Cl-. Transport-enhancement effects of anions were ascribed to competition between inorganic anions and tetracycline for deposition sites on sand surfaces. However, when Ca2+ was the counterion, the differences in the breakthrough curve of tetracycline among three inorganic anions (i.e., SO42-, NO3- and Cl-) were very small. In this case, the transport-inhibiting effects of anions could be counterbalanced by the transport-enhancement effects of the cation-bridging effect. Also, the two-site nonequilibrium transport model was applied to analyze the transport data. Findings from this study improve our understanding of the transport of tetracycline in saturated aquifer materials.

The effect of divalent metal cations on the αv integrin binding site is ligand and integrin specific

The binding of orthosteric ligands to integrins requires the presence of divalent metal cations bound to metal ion-binding sites located in the I domains of the integrin α and β subunits. In this study the influence of the type and concentration of divalent metal cation present was investigated on a single arginyl-glycinyl-aspartic acid (RGD) ligand across the αv integrin sub-family and single αv integrin (αvβ6) with different ligands. These relationships were determined using radioligand binding studies completed with [3H] ligands and purified αv integrin protein preparations. The binding of [3H]compound 1 to the RGD site on individual αv integrins demonstrated a unique profile in relation to the type and concentration of divalent metal cation present. The use of physiological concentrations of Mg2+ and Ca2+ in simulated lung fluid altered the αv integrin selectivity profile of [3H]compound 1 in terms of affinity and the level of receptor occupancy. In addition, different RGD ligands for the αvβ6 integrin behaved differently under the same divalent metal cation conditions. In conclusion, this study demonstrates the need to determine the individual relationship between RGD ligands and the integrins they may engage in vivo, especially when determining selectivity profiles for potential RGD-mimetic small molecule therapeutics, with organ and disease state also considered.

Species Difference in Sensitivity of Human and Mouse P2X7 Receptors to Inhibitory Effects of Divalent Metal Cations.

P2X7 receptor (P2X7R), a purinergic receptor, is involved in pathophysiological events such as inflammation and cell death, and thus is an attractive target for therapeutic approaches. It is reported that divalent metal cations (DMCs) inhibit P2X7R activation and that there are species differences in their inhibitory effects. To extrapolate the findings in experimental animals to humans, these species differences have to be clarified, but species differences in the sensitivity of P2X7R to DMCs between man and mouse have not been demonstrated. Here we performed direct comparison of the inhibitory effects of DMCs on human and mouse P2X7R activation. Cell lines constitutively expressing human and mouse P2X7R were used, and their P2X7R activation was evaluated as means of YO-PRO-1 dye uptake. MgCl2, NiCl2, ZnCl2, CuCl2 and CaCl2 dose-dependently decreased agonist-induced YO-PRO-1 uptake via both human and mouse P2X7Rs. Apparent differences in the inhibitory profiles for NiCl2 and CaCl2 between them were found, and the IC50 values of DMCs were in the order of CaCl2>MgCl2>NiCl2≈ZnCl2>CuCl2 for both human and mouse P2X7Rs. In this study, we demonstrate that human P2X7R exhibits different sensitivity to nickel and calcium compared with the case of the mouse one, while there is no species difference in the sensitivity of their P2X7Rs to magnesium, zinc and copper, suggesting that the effects of magnesium, zinc and copper on P2X7R-associated pathophysiological events in humans might be predicted from those in mice.

Inhibitory effect of divalent metal cations on zinc uptake via mouse Zrt-/Irt-like protein 8 (ZIP8)

AimsThere is controversy regarding the substrate specificity of ZIP8, a ZIP isoform, involved in regulation of extra- and intracellular zinc levels. Here, we investigated the inhibitory effects of divalent metal cations on zinc uptake via mouse ZIP8 (mZIP8). Main methodsmZIP8 cDNA was transfected into HEK293T cells by a lipofection method, and its functional expression was evaluated by immunocytochemistry, Western blotting and 65Zn (65ZnCl2) uptake measurement. Key findingsTransfection of mZIP8 cDNA into HEK293T cells induced expression of mZIP8 in the cells, and increased zinc uptake. mZIP8-mediated zinc uptake depended on extracellular bicarbonate, and the Michaelis constant for the uptake was estimated to be 8.48±2.46μM. In the inhibition study, iron and cadmium competitively, and cobalt, nickel and copper non-competitively inhibited the mZIP8-mediated zinc uptake, the inhibition constants being calculated to be 3.37, 55.5, 80.6, 198 and 48.3μM, respectively. In contrast, magnesium and manganese at concentrations of up to 1500 and 200μM, respectively, had no inhibitory effect on the zinc uptake via mZIP8. SignificanceIn this study, we reveal that the inhibition profiles of divalent metal cations as to zinc uptake via mZIP8 apparently differ from those for mZIP1, especially in the affinity and inhibition manner of nickel. These findings should contribute to identification of ZIP isoforms involved in total cellular zinc transport.

Effect of Divalent Metal Cations on Contaminant Removal by Bicarbonate-Form Anion Exchange Resin

This work investigated the role of divalent metal cations (Mg2+, Ca2+, and Cd2+) and subsequent precipitation or complexation on decreased contaminant removal by bicarbonate-form anion exchange resin (AER-HCO3) relative to chloride-form AER (AER-Cl). The results showed that the removal of dissolved organic carbon and nitrate was lower for AER-HCO3 than AER-Cl, and contaminant removal by AER-HCO3 was affected by the presence of metal cation. For instance, magnesium and cadmium exhibited the greatest and least interference, respectively, with contaminant removal by AER-HCO3. The results suggested that precipitation was not the cause of decreased contaminant removal by AER-HCO3, and instead implied that complex formation between the contaminant and divalent metal was responsible for differences in removal by AER

The effect of divalent metal cations on zinc uptake by mouse Zrt/Irt-like protein 1 (ZIP1)

AimIn this study, we evaluated the effect of divalent metal cations on zinc uptake via mouse Zrt/Irt-like protein 1 (mZIP1), a ubiquitously expressed zinc transporter, which plays a role in maintenance of cellular zinc homeostasis, using HEK293T cells overexpressing it. Main methodsmZIP1 cDNA, which was cloned from mouse microglia, was transfected into HEK293T cells by a lipofection method, and its functional expression was confirmed by Western blotting and immunocytochemical analyses, and 65Zn (65ZnCl2) uptake. Key findings65Zn uptake by mZIP1 cDNA-transfected cells time-dependently increased compared with that by mock cells, indicating functional expression of mZIP1. mZIP1-mediated 65Zn uptake showed clear saturable kinetics consisting of a single component with a Michaelis constant of 5.88μM. FeCl2 and NiCl2 competitively inhibited the 65Zn uptake, the inhibition constants (Ki) being estimated to be 0.92 and 28.6μM, respectively. In addition, CoCl2 and CdCl2 showed non-competitive inhibition of mZIP1-mediated 65Zn uptake, the Ki values being 219 and 32.5μM, respectively. On the other hand, CuCl2 also significantly decreased the uptake, but the inhibition mode could not evaluate because of its low solubility, while MnCl2 and MgCl2 had no effect on 65Zn uptake via mZIP1. SignificanceIron, nickel, cobalt and cadmium act as inhibitors of mZIP1, the affinity order being iron>zinc>nickel=cadmium>cobalt, and copper might also act as an inhibitor, while manganese and magnesium are not recognized by mZIP1. These findings provide valuable information as to the contribution of mZIP1 to total cellular zinc transport.

Antibacterial Activity of Probiotic Lactobacillus plantarum HK01: Effect of Divalent Metal Cations and Food Additives on Production Efficiency of Antibacterial Compounds

One hundred and sixty lactic acid bacteria, isolated from Iranian traditional dairy products, were screened for antibacterial potential. Among them, an isolate showing remarkable antibacterial activity against both Staphylococcus aureus (PTCC 1112) and Escherichia coli (PTCC 1338) was selected based on minimum inhibitory concentration (AU/mL). The morphological and biochemical characteristics of the isolate matched the literature description about genus Lactobacillus. Partial sequencing of 16S rRNA gene and its alignment with other Lactobacillus strains revealed that the isolate was closely related to the Lactobacillus plantarum. The isolate also exhibited the highest similarity (>99%) to L. plantarum. We thus tentatively classified the bacterial isolate as L. plantarum HK01. The antibacterial active compound from HK01 strain remained stable for 45min at 121°C, and it reached a maximum activity at the end of log phase and the early part of stationary phase. The antibacterial activity of the test isolate, its probiotic properties and production efficacy through addition of some divalent metal cations and food additives were studied as well. The study of bile salt hydrolase (BSH) activity as a function of growth revealed that HK01 strain hydrolysing up to 5% of sodium salt of glycodeoxycholic acid, correlated with the presence of bsh gene in the isolate. HK01 strain showed high resistance to lysozyme, good adaptation to simulated gastric juice and a moderate bile tolerance. Results obtained from simulated gastric juice conditions showed no significant difference occured during the 70min. HK01 strain was classified as a strain with low hydrophobicity (34.2%). Addition of trisodium citrate dehydrates as a food-grade chelator of divalent cations restored antibacterial compound production in MRS broth. Antibacterial compounds of L. plantarum HK01 endured treatment with 10g/L of SDS, Tween 20, Tween 80 and urea. Concerning food additives, the results demonstrated that antibacterial compound production by L. plantarum HK01 was influenced by the presence of surfactants, EDTA, KCl and sodium citrate.

Negative effect of divalent metal cations on production of gassericin T, a bacteriocin produced by Lactobacillus gasseri, in milk-based media

A broad-spectrum bacteriocin named gassericin T is produced by Lactobacillus gasseri LA158 in MRS broth, but is minimally produced in milk-based media. Gassericin T production in MRS broth was specifically inhibited by adding divalent metal cations. Such inhibition of gassericin T production depended on the concentration of divalent cations. The addition of trisodium citrate dihydrate (TSC), which is a food-grade chelator of divalent cations, restored gassericin T production both in modified MRS broth containing divalent cations and in milk-based medium. In modified MRS broth, 50 mmol L −1 TSC promoted an over-production of gassericin T. Furthermore, it was confirmed that TSC had a synergistic antibacterial effect with gassericin T. In this study, a cheese-whey-based medium, supplemented with proteose peptone, TSC, and Tween 80, was developed for gassericin T production. These results may contribute to the effective use of bacteriocins for food preservation.

Effects of divalent metal cations on lovastatin biosynthesis from Aspergillus terreus in chemically defined medium

Effects of six divalent metal cations: Fe2+, Ca2+, Zn2+, Mg2+, Cu2+and Mn2+ on fungal cell growth and lovastatin biosynthesis were investigated by submerged cultivation of Aspergillus terreus in a modified chemically defined medium. The influences of different initial concentrations of the above six metal cations were also examined at 1, 2, and 5 mM, respectively. Cu2+ apparently inhibited the cell growth, but had no influence on biosynthesis of lovastatin. All of Fe2+, Ca2+, Zn2+, Mg2+ and Mn2+ promoted the cell growth and lovastatin biosynthesis in different extents. The highest biomass of 13.8 ± 0.5 g l−1 and specific lovastatin titres of 49.2 ± 1.4 mg gDCW−1 were obtained at the level of 2 and 5 mM in the presence of Zn2+, respectively. The values were improved double and 14.4-fold. Excess Zn2+ inhibited the cell growth, but enhanced lovastatin biosynthesis with an increment of 17.6 mg l−1 per mM. The interactions of all metal cations slightly inhibited the lovastatin production comparing with the existence of Zn2+, Fe2+ and Mg2+ solely, yet remarkably improved the cell growth. These results suggest that the divalent metal ions Zn2+ or Fe2+ influence the production by regulating the action of key enzymes such as LovD or LovF in lovastatin biosynthesis.

Identification of ADAMTS13 Epitopes Required for Binding to von Willebrand Factor Using Lambda Phage Surface Display.

The metalloprotease ADAMTS13 cleaves multimeric von Willebrand factor (VWF) to regulate VWF-mediated thrombus formation. We planned to search core epitopes of ADAMTS13 that is required for its binding to VWF. We constructed a random cDNA fragment library expressing various peptides of ADAMTS13 on the surface of lambda phage and screened the library using immobilized VWF as a probe. After the first screening, the C-terminus of the spacer domain from Arg670 to Glu684 (termed as epitope-1) and the middle of the cysteine-rich domain from Arg484 to Arg507 (epitope-2) were determined as epitopes. When we added the synthetic epitope-1 peptide to the second screening, a new site, from Pro618 to Glu641 (epitope-3), was found in the middle of spacer domain. While the presence of synthetic epitope-2 peptide did not affect the subsequent screening, the presence of epitope-3 peptide enhanced the isolation of clones encoding epitope-1. These results suggest that ADAMTS13 epitopes-1, -2 and -3 may interact with each other for their binding to VWF. From screening in the presence of any combination or all of the three synthetic peptides, however, no new VWF binding site was uncovered. To examine the effect of divalent metal cations on the binding of ADAMTS13 epitopes to immobilized VWF, screening was carried out in the presence or absence of 5 mM of EDTA. No new epitope site was found. We next explored inhibitory effect of the synthetic epitope peptides on ADAMTS13 protease activity using recombinant ADAMTS13 and FRETS-VWF73 as a substrate. Synthetic epitopes-2 and -3 peptides markedly inhibited the cleavage of VWF by ADAMTS13, while the synthetic epitope-1 peptide did not as efficiently as epitopes-2 and -3. The stronger inhibitory effect of epitope-3 peptide than that of epitope-1 peptide was confirmed by SDS-agarose gel electrophoresis analysis of cleavage products of denatured multimeric VWF molecules by recombinant ADAMTS13. This was consistent with the dissociation constants for the three synthetic peptides with immobilized VWF determined by surface plasmon resonance, in which epitopes-2 and -3 have higher affinities for VWF than that of epitope-1. The results described above suggest that ADAMTS13 may initially bind to immobilized VWF through the sites of epitope-1 and epitope-2 with relatively weak affinity. The binding of epitope-1 to VWF may subsequently induce the conformational change of VWF, thereby exposing a binding site for epitope-3 for the efficient catalytic cleavage of VWF by ADAMTS13.

Identification of a novel thyroid hormone‐sulfating cytosolic sulfotransferase, SULT1 ST5, from zebrafish

By employing RT-PCR in conjunction with 3'-RACE, a full-length cDNA encoding a novel zebrafish cytosolic sulfotransferase (SULT) was cloned and sequenced. Sequence analysis revealed that this zebrafish SULT (designated SULT1 ST5) is, at the amino acid sequence level, close to 50% identical to human and dog SULT1B1 (thyroid hormone SULT). A recombinant form of zebrafish SULT1 ST5 was expressed using the pGEX-2TK bacterial expression system and purified from transformed BL21 (DE3) cells. Purified zebrafish SULT1 ST5 migrated as a 34 kDa protein and displayed substrate specificity for thyroid hormones and their metabolites among various endogenous compounds tested. The enzyme also exhibited sulfating activities toward some xenobiotic phenolic compounds. Its pH optima were 6.0 and 9.0 with 3,3',5-triiodo-l-thyronine (l-T3) as substrate and 6.0 with beta-naphthol as substrate. Kinetic constants of the enzyme with thyroid hormones and their metabolites as substrates were determined. Quantitative evaluation of the regulatory effects of divalent metal cations on the l-T3-sulfating activity of SULT1 ST5 revealed that Fe2+, Hg2+, Co2+, Zn2+, Cu2+, Cd2+ and Pb2+ exhibited dramatic inhibitory effects, whereas Mn2+ showed a significant stimulation. Developmental stage-dependent expression experiments revealed a significant level of expression of this novel zebrafish thyroid hormone-sulfating SULT at the beginning of the hatching period during embryogenesis, which gradually increased to a high level of expression throughout the larval stage into maturity.

Influence of divalent cations on the structural thermostability and thermal inactivation kinetics of class II xylose isomerases

The effects of divalent metal cations on structural thermostability and the inactivation kinetics of homologous class II d-xylose isomerases (XI; EC 5.3.1.5) from mesophilic (Escherichia coli and Bacillus licheniformis), thermophilic (Thermoanaerobacterium thermosulfurigenes), and hyperthermophilic (Thermotoga neapolitana) bacteria were examined. Unlike the three less thermophilic XIs that were substantially structurally stabilized in the presence of Co2+ or Mn2+ (and Mg2+ to a lesser extent), the melting temperature [(Tm) approximately 100 degrees C] of T. neapolitana XI (TNXI) varied little in the presence or absence of a single type of metal. In the presence of any two of these metals, TNXI exhibited a second melting transition between 110 degrees C and 114 degrees C. TNXI kinetic inactivation, which was non-first order, could be modeled as a two-step sequential process. TNXI inactivation in the presence of 5 mm metal at 99-100 degrees C was slowest in the presence of Mn2+[half-life (t(1/2)) of 84 min], compared to Co2+ (t(1/2) of 14 min) and Mg2+ (t(1/2) of 2 min). While adding Co2+ to Mg2+ increased TNXI's t(1/2) at 99-100 degrees C from 2 to 7.5 min, TNXI showed no significant activity at temperatures above the first melting transition. The results reported here suggest that, unlike the other class II XIs examined, single metals are required for TNXI activity, but are not essential for its structural thermostability. The structural form corresponding to the second melting transition of TNXI in the presence of two metals is not known, but likely results from cooperative interactions between dissimilar metals in the two metal binding sites.

The role of thioredoxin and disulfide isomerase in the expression of the snake venom thrombin-like enzyme calobin in Escherichia coli BL21 (DE3)

Thrombin-like enzymes (TLEs) are studied widely because of their therapeutic potential in myocardial infarction and thrombotic diseases. But they are always produced in Escherichia coli BL21 (DE3) as inclusion bodies because they are single chain Cys-rich proteins. In this work, coexpressing of thioredoxin (TrxA) largely increased the solubility of calobin, one of the TLEs from korea viper Agkistrodon caliginosus, but soluble calobin-T had poor enzyme activity. Disulfide isomerase (DsbC) was introduced into the host cell and coexpressed with calobin in the presence of TrxA, the result was that both the solubility and enzyme activity of calobin-TD were higher than those of calobin-T. Although recombinant calobins exhibited the enzyme of hydrolyzing the fibrinogen, they lost clotting activity to the substrate. Recombinant calobin-TD remained poor amidolytic activity, the effects of divalent metal cations and various inhibitors on this activity were similar to those of native calobin nevertheless, suggesting that calobin-TD exhibited the characteristics of serine protease especially of trypsin-like serine protease.

Differential roles of human monoamine (M)-form and simple phenol (P)-form phenol sulfotransferases in drug metabolism.

Cytosolic sulfotransferases (STs) are traditionally known as Phase II drug-metabolizing or detoxifying enzymes that facilitate the removal of drugs and other xenobiotic compounds. In this study, we carried out a systematic investigation on the sulfation of drug compounds by two major human phenol STs (PSTs), the monoamine (M)-form and simple phenol (P)-form PSTs. Activity data obtained showed the differential substrate specificity of the two enzymes for the thirteen drug compounds tested. Kinetic studies revealed that the M-form PST displayed stereoselectivity for the chiral drug, isoproterenol. The effects of divalent metal cations on the activity of the M-form and P-form PSTs toward representative drug compounds were quantitatively evaluated. Results obtained indicated that the drug-sulfating activities of the two human PSTs were partially or completely inhibited or stimulated by the ten divalent metal cations tested at a 5 mM concentration. The two enzymes appeared to be less sensitive to the effects of physiologically more abundant metal cations such as Mg(2+) and Ca(2+), but more sensitive to the detrimental effects of other metal cations that may enter the body as environmental contaminants.

Regulatory effects of divalent metal cations on human cytosolic sulfotransferases.

Cytosolic sulfotransferases (STs), traditionally viewed as Phase II drug-metabolizing or detoxifying enzymes, are increasingly being implicated in the metabolism of endogenous biologically-active molecules. Except for studies on changes in their levels of expression and activity in the early stage of development in mammals, very little is known about how these enzymes are regulated. In this study, the regulatory effects of divalent metal cations on the activity of human cytosolic STs were quantitatively evaluated. Results obtained indicate that all nine human cytosolic STs examined are partially or completely inhibited/stimulated by the ten divalent metal cations tested at 10 mM concentration. Compared with the other metal cations, the inhibitory or stimulatory effect of Mg2+ and Ca2+ on the activities of the human cytosolic STs appeared to be relatively smaller. Concentration-dependent effects of the divalent metal cations were further examined. The IC50 or EC50 values determined for different divalent metal cations were mostly above their normal physiological concentration ranges. In a few cases, however, IC50 values close to the physiological concentrations of certain divalent metal cations were observed. Using the monoamine (M)-form phenol ST (PST) as a model, it was demonstrated that the K(m) for dopamine changed only slightly with increasing concentrations of Cd2+, whereas the V(max) was dramatically decreased.

Effect of heavy metals on nitrate assimilation in the eukaryotic microalga Chlamydomonas reinhardtii

The effect of divalent metal cations (Cd 2+, Cu 2+, Zn 2+, Fe 2+, Co 2+) on nitrate uptake and the effect of Cd 2+ on nitrogen and sulphur assimilation enzymes were studied in the eukaryotic alga Chlamydomonas reinhardtii. Nitrate consumption was not inhibited by metal concentrations below 100 μM; however, concentrations exceeding 150 μM Cd 2+, Cu 2+ or Zn 2+ induced 75 % inhibition, whereas Fe 2+ or Co 2+ did not significantly affect nitrate uptake. Among the enzymes of nitrogen and sulphur assimilatory pathways, 2-d exposure of C. reinhardtii cells to 100 μM Cd 2+ did not affect ferredoxin-nitrite reductase (EC 1.7.7.1), ferredoxin-glutamate synthase (EC 1.4.7.1), NADH-glutamate synthase (EC 1.4.1.14) and O-acetyl-L-serine(thiol)lyase (EC 4.2.99.8) activities, but a 45 % inhibition of glutamine synthetase activity (EC 6.3.1.2) was observed. This inhibition increased with Cd 2+ concentration and was reverted by adding Mn 2+ to the reaction mixture, which can be interpreted as the result of a competitive inhibition of Mn 2+ in glutamine synthetase by high cadmium concentration.

Modulatory effect of divalent metal cations on the phosphotyrosine activity of the frog liver acid phosphatase.

Frog liver acid phosphatase hydrolyzes phosphotyrosine at acidic pH optimum. Mn2+, Ca2+ and Mg2+ (but not Zn2+) ions modulate this activity by shifting its pH optimum to physiological pH. This effect is not observed when p-nitrophenylphosphate is used as a substrate. Phosphoserine and phosphothreonine are not hydrolyzed under the same conditions.

Effects of Divalent Metal Cations and Resistance Mechanisms of the Cyanobacterium Synechococcus SP. Strain PCC 7942

Cyanobacteria exhibit an extraordinary resistance to many environmental factors including nutrient limitation, changes in hydrogen ion concentration, temperature, and light extremes. A better understanding of the biological effects and response mechanisms of cyanobacteria to heavy metal exposure could be used to develop these bacteria for use in bioremediation. Synechococcus sp. strain PCC 7942 expresses messenger RNA for the stress protein GroEL and for the metal-binding protein metallothionein in response to a wide range of divalent metal ion concentrations. Although groEL is expressed at low levels regardless of environmental conditions, a high rate of transcription is initiated within 15 minutes following exposure to divalent metal cations at concentrations ranging from 10 µM to 100 µM for copper and zinc, and concentrations as low as 1 µM for cadmium. Transcript levels return to normal within one hour following exposure to each metal. Induction of the metallothionein operon also occurs within 15 minutes of these exposures. We speculate that these resistance mechanisms are working together to protect the cell from damage.