Presence Of Different Divalent Cations Research Articles

NH125 Sensitizes Staphylococcus aureus to Cell Wall-Targeting Antibiotics through the Inhibition of the VraS Sensor Histidine Kinase.

Staphylococcus aureus utilizes the two-component regulatory system VraSR to receive and relay environmental stress signals, and it is implicated in the development of bacterial resistance to several antibiotics through the upregulation of cell wall synthesis. VraS inhibition was shown to extend or restore the efficacy of several clinically used antibiotics. In this work, we study the enzymatic activity of the VraS intracellular domain (GST-VraS) to determine the kinetic parameters of the ATPase reaction and characterize the inhibition of NH125 under in vitro and microbiological settings. The rate of the autophosphorylation reaction was determined at different GST-VraS concentrations (0.95 to 9.49 μM) and temperatures (22 to 40°C) as well as in the presence of different divalent cations. The activity and inhibition by NH125, which is a known kinase inhibitor, were assessed in the presence and absence of the binding partner, VraR. The effects of inhibition on the bacterial growth kinetics and gene expression levels were determined. The GST-VraS rate of autophosphorylation increases with temperature and with the addition of VraR, with magnesium being the preferred divalent cation for the metal-ATP substrate complex. The mechanism of inhibition of NH125 was noncompetitive in nature and was attenuated in the presence of VraR. The addition of NH125 in the presence of sublethal doses of the cell wall-targeting antibiotics carbenicillin and vancomycin led to the complete abrogation of Staphylococcus aureus Newman strain growth and significantly decreased the gene expression levels of pbpB, blaZ, and vraSR in the presence of the antibiotics. IMPORTANCE This work characterizes the activity and inhibition of VraS, which is a key histidine kinase in a bacterial two-component system that is involved in Staphylococcus aureus antibiotic resistance. The results show the effect of temperature, divalent ions, and VraR on the activity and the kinetic parameters of ATP binding. The value of the KM of ATP is vital in designing screening assays to discover potent and effective VraS inhibitors with high translational potential. We report the ability of NH125 to inhibit VraS in vitro in a noncompetitive manner and investigate its effect on gene expression and bacterial growth kinetics in the presence and absence of cell wall-targeting antibiotics. NH125 effectively potentiated the effects of the antibiotics on bacterial growth and altered the expression of the genes that are regulated by VraS and are involved in mounting a resistance to antibiotics.

Bivalent metal ions induce formation of α-synuclein fibril polymorphs with different cytotoxicities

α-Synuclein (α-Syn) aggregates are key components of intracellular inclusion bodies characteristic of Parkinson’s disease (PD) and other synucleinopathies. Metal ions have been considered as the important etiological factors in PD since their interactions with α-Syn alter the kinetics of fibrillation. In the present study, we have systematically explored the effects of Zn2+, Cu2+, Ca2+, and Mg2+ cations on α-Syn fibril formation. Specifically, we determined fibrillation kinetics, size, morphology, and secondary structure of the fibrils and their cytotoxic activity. While all cations accelerate fibrillation, we observed distinct effects of the different ions. For example, Zn2+ induced fibrillation by lower tlag and higher kapp and formation of shorter fibrils, while Ca2+ ions lead to formation of longer fibrils, as evidenced by dynamic light scattering and atomic force microscopy studies. Additionally, the morphology of formed fibrils was different. Circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopies revealed higher contents of β-sheets in fibrils. Interestingly, cell viability studies indicated nontoxicity of α-Syn fibrils formed in the presence of Zn2+ ions, while the fibrils formed in the presence of Cu2+, Ca2+, and Mg2+ were cytotoxic. Our results revealed that α-Syn fibrils formed in the presence of different divalent cations have distinct structural and cytotoxic features.

Preparation and structural investigation of Polyethylene glycol (PEG) / nano-ferrite composites

Polyethylene glycol (PEG)/nano-ferrite composites have been prepared by using CoFe2O4, CuFe2O4, Co0.5Cu0.5Fe2O4 and MgFe2O4 ferrite nano-particles synthesized by citrate precursor method along with PEG with different percentages. Ferrite samples have been characterized by X-ray diffraction (XRD) to confirm the formation of pure spinel ferrite phase and, transmission electron microscopy (TEM) to ensure that the average particle size is within the nano-scale. Thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermographs of the ferrite samples have been used to ensure the complete formation of pure ferrites at temperatures above 800oC. The ferrites and their composites with PEG, have been investigated by FTIR spectroscopy. The main bands of ferrites and PEG have been clearly displayed in agreement with literature. A systematic shift of the bands has been observed upon adding PEG. The magnetic properties have been explored by using the vibrating sample magnetometer (VSM). Where the values of of saturation magnetization (Ms), remnant magnetization (Mr) and coercive field (Hc) for pure ferrite and composite samples vary with the presence of different divalent cations which have different magnetic moment. Whereas, Hc values remain constant as obtained in pure ferrites regardless the ratio of PEG. The obtained values of Hc are comparable with those in literature, which can be used in electromagnetic wave attenuation.

Comparative analysis of the metal-dependent structural and functional properties of mouse and human SMP30.

Senescence Marker Protein (SMP30) is a metalloenzyme that shows lactonase activity in the ascorbic acid (AA) biosynthesis pathway in non-primate mammals such as a mouse. However, AA biosynthesis does not occur in the primates including humans. Several studies have shown the role of SMP30 in maintaining calcium homeostasis in mammals. In addition, it is also reported to have promiscuous enzyme activity with an organophosphate (OP) substrate. Hence, this study aims to recombinantly express and purify the SMP30 proteins from both mouse and human, and to study their structural alterations and functional deviations in the presence of different divalent metals. For this, mouse SMP30 (MoSMP30) as well as human SMP30 (HuSMP30) were cloned in the bacterial expression vector. Proteins were overexpressed and purified from soluble fractions as well as from inclusion bodies as these proteins were expressed largely in insoluble fractions. The purified proteins were used to study the folding conformations in the presence of different divalent cations (Ca2+, Co2+, Mg2+, and Zn2+) with the help of circular dichroism (CD) spectroscopy. It was observed that both MoSMP30 and HuSMP30 acquired native folding conformations. To study the metal-binding affinity, dissociation constant (Kd values) were calculated from UV-VIS titration curve, which showed the highest affinity of MoSMP30 with Zn2+. However, HuSMP30 showed the highest affinity with Ca2+, suggesting the importance of HuSMP30 in maintaining calcium homeostasis. Enzyme kinetics were performed with γ-Thiobutyrolactone and Demeton-S in the presence of different divalent cations. Interestingly, both the proteins showed lactonase activity in the presence of Ca2+. In addition, MoSMP30 and HuSMP30 also showed lactonase activity in the presence of Co2+ and Zn2+ respectively. Moreover, both the proteins showed OP hydrolase activities in the presence of Ca2+ as well as Zn2+, suggesting the metal-dependent promiscuous nature of SMP30.

Identification of zebrafish steroid sulfatase and comparative analysis of the enzymatic properties with human steroid sulfatase

Steroid sulfatase (STS) plays an important role in the regulation of steroid hormones. Metabolism of steroid hormones in zebrafish has been investigated, but the action of steroid sulfatase remains unknown. In this study, a zebrafish sts was cloned, expressed, purified, and characterized in comparison with the orthologous human enzyme. Enzymatic assays demonstrated that similar to human STS, zebrafish Sts was most active in catalyzing the hydrolysis of estrone-sulfate and estradiol-sulfate, among five steroid sulfates tested as substrates. Kinetic analyses revealed that the Km values of zebrafish Sts and human STS differed with respective substrates, but the catalytic efficiency as reflected by the Vmax/Km appeared comparable, except for DHEA-sulfate with which zebrafish Sts appeared less efficient. While zebrafish Sts was catalytically active at 28 °C, the enzyme appeared more active at 37 °C and with similar Km values to those determined at 28 °C. Assays performed in the presence of different divalent cations showed that the activities of both zebrafish and human STSs were stimulated by Ca2+, Mg2+, and Mn2+, and inhibited by Zn+2 and Fe2+. EMATE and STX64, two known mammalian steroid sulafatase inhibitors, were shown to be capable of inhibiting the activity of zebrafish Sts. Collectively, the results obtained indicated that zebrafish Sts exhibited enzymatic characteristics comparable to the human STS, suggesting that the physiological function of STS may be conserved between zebrafish and humans.

Evaluating the nuclease activity of Pseudomonas exotoxin A

Pseudomonas exotoxin A (PE) is a protein toxin secreted by Pseudomonas aeruginosa. The toxin is remarkably potent, and believed to be the major virulence factor of P. aeruginosa. PE inhibits protein synthesis by inactivating elongation factor 2 (EF2), the protein that advances the ribosome along the mRNA during translation. Cell with inactive EF2 are unable to synthesize proteins, which leads to apoptosis. Recent studies have indicated that, in addition to inhibition of protein synthesis, PE has also functions as a nuclease. The purpose of the experiments described here is to verify this unusual claim and characterize the nuclease activity of PE using only the catalytic fragment of the toxin. We have conducted basic time‐course and concentration assays, and have confirmed a low level of nuclease activity from PE. We are currently examining cleavage in the presence of different divalent cations (Ba2+, Sr2+, Mn2+, Co2+, Ca2+, Mg2+ and Zn2+). We have also tested a fluorescence‐based assay to observe cleavage of DNA in real‐time. Initial experiments using DNase I have been successful, and we hope to use this method to study PE in the near future.Support or Funding InformationResearch reported in this poster was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R25GM058264. Additional support for this research comes from Towson University, the Jess and Mildred Fisher College of Science and Mathematics, Graduate Studies and the Department of Biological Sciences.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Improving Properties of a Novel β-Galactosidase from Lactobacillus plantarum by Covalent Immobilization.

A novel β-galactosidase from Lactobacillus plantarum (LPG) was over-expressed in E. coli and purified via a single chromatographic step by using lowly activated IMAC (immobilized metal for affinity chromatography) supports. The pure enzyme exhibited a high hydrolytic activity of 491 IU/mL towards o-nitrophenyl β-d-galactopyranoside. This value was conserved in the presence of different divalent cations and was quite resistant to the inhibition effects of different carbohydrates. The pure multimeric enzyme was stabilized by multipoint and multisubunit covalent attachment on glyoxyl-agarose. The glyoxyl-LPG immobilized preparation was over 20-fold more stable than the soluble enzyme or the one-point CNBr-LPG immobilized preparation at 50 °C. This β-galactosidase was successfully used in the hydrolysis of lactose and lactulose and formation of different oligosaccharides was detected. High production of galacto-oligosaccharides (35%) and oligosaccharides derived from lactulose (30%) was found and, for the first time, a new oligosaccharide derived from lactulose, tentatively identified as 3'-galactosyl lactulose, has been described.

Supramolecular assemblies of phenyl-pyridyl-triazolopyridine and β-cyclodextrin as sensor of divalent cations in aqueous solution.

The chemosensor 3-phenyl-7-(pyrid-2-yl)-[1,2,3]triazolo[1,5-a]pyridine (PhPTP) used in combination with two different cyclodextrins, enable its solubilization and stabilization in aqueous solution. The behavior of the inclusion complex, and its binding ability in both cyclodextrins were investigated by means of absorption and fluorescence spectroscopy. The best results were obtained for PhPTP-DMβCD assembly, and its orientation in the DMβCD nano cavity was obtained by 2D-NMR. This inclusion geometry was confirmed by docking studies. The binary complex was proved as chemosensor upon the presence of different divalent cations in aqueous solutions. The PhPTP-DMβCD system, displays a high sensitivity for Fe(2+) by fluorescence quenching in neutral aqueous solution even in the presence of other metals showing high selectivity towards Fe(2+).

Mechanism of Nisin, Pediocin 34, and Enterocin FH99 Resistance in Listeria monocytogenes.

Nisin-, pediocin 34-, and enterocin FH99-resistant variants of Listeria monocytogenes ATCC 53135 were developed. In an attempt to clarify the possible mechanisms underlying bacteriocin resistance in L. monocytogenes ATCC 53135, sensitivity of the resistant strains of L. monocytogenes ATCC 53135 to nisin, pediocin 34, and enterocin FH99 in the absence and presence of different divalent cations was assessed, and the results showed that the addition of divalent cations significantly reduced the inhibitory activity of nisin, pediocin 34, and enterocin FH99 against resistant variants of L. monocytogenes ATCC 53135. The addition of EDTA, however, restored this activity suggesting that the divalent cations seem to affect the initial electrostatic interaction between the positively charged bacteriocin and the negatively charged phospholipids of the membrane. Nisin-, pediocin 34-, and enterocin-resistant variants of L. monocytogenes ATCC 53135 were more resistant to lysozyme as compared to the wild-type strain both in the presence as well as absence of nisin, pediocin 34, and enterocin FH99. Ultra structural profiles of bacteriocin-sensitive L. monocytogenes and its bacteriocin-resistant counterparts revealed that the cells of wild-type strain of L. monocytogenes were maximally in pairs or short chains, whereas, its nisin-, pediocin 34-, and enterocin FH99-resistant variants tend to form aggregates. Results indicated that without a cell wall, the acquired nisin, pediocin 34, and enterocin FH99 resistance of the variants was lost. Although the bacteriocin-resistant variants appeared to lose their acquired resistance toward nisin, pediocin 34, and enterocin FH99, the protoplasts of the resistant variants appeared to be more resistant to bacteriocins than the protoplasts of their wild-type counterparts.

Crystal Structure, Biochemical and Genetic Characterization of Yeast and E. cuniculi TAF II5 N-terminal Domain: Implications for TFIID Assembly

General transcription factor TFIID plays an essential role in transcription initiation by RNA polymerase II at numerous promoters. However, understanding of the assembly and a full structural characterization of this large 15 subunit complex is lacking. TFIID subunit TAF II5 has been shown to be present twice in this complex and to be critical for the function and assembly of TFIID. Especially, the TAF II5 N-terminal domain is required for its incorporation within TFIID and immuno-labelling experiments carried out by electron microscopy at low resolution have suggested that this domain might homodimerize, possibly explaining the three-lobed architecture of TFIID. However, the resolution at which the electron microscopy (EM) analyses were conducted is not sufficient to determine whether homodimerization occurs or whether a more intricate assembly implying other subunits is required. Here we report the X-ray structures of the fully evolutionary conserved C-terminal sub-domain of the TAF II5 N terminus, from yeast and the mammalian parasite Encephalitozoon cuniculi. This sub-domain displays a novel fold with specific surfaces having conserved physico-chemical properties that can form protein–protein interactions. Although a crystallographic dimer implying one of these surfaces is present in one of the crystal forms, several biochemical analyses show that this sub-domain is monomeric in solution, even at various salt conditions and in presence of different divalent cations. Consequently, the N-terminal sub-domain of the TAF II5 N terminus, which is homologous to a dimerization motif but has not been fully conserved during evolution, was studied by analytical ultracentrifugation and yeast genetics. Our results show that this sub-domain dimerizes at very high concentration but is neither required for yeast viability, nor for incorporation of two TAF II5 molecules within TFIID and for the assembly of this complex. Altogether, although our results do not argue in favour of a homodimerization of the TAF II5 N-terminal domain, our structural analyses suggest a role for this domain in assembly of TFIID and its related complexes SAGA, STAGA, TFTC and PCAF.

Divalent Cation Interactions with Oligogalacturonides

The conformational properties of high and low molecular weight galacturonides were investigated in relation to the ability of oligomers with degree of polymerization >10 to act as elicitors of plant defense mechanisms. Oligomers from polygalacturonate were obtained by means of enzymatic hydrolysis. Two fractions exhibiting high and low average degrees of polymerization were isolated by solvent fractionation and characterized by means of electrospray mass spectrometry. The conformational behaviors of the two fractions were investigated in the presence of different divalent cations using circular dichroism. Calcium, copper, and zinc ions were able to induce a conformational transition in both fractions. When in the presence of the high molecular weight fraction, copper and zinc ions were much more effective than calcium ions, whereas the efficiency was much reduced with low molecular weight oligomers.

Membrane Fusion and the Lamellar-to-Inverted-Hexagonal Phase Transition in Cardiolipin Vesicle Systems Induced by Divalent Cations

The polymorphic phase behavior of bovine heart cardiolipin (CL) in the presence of different divalent cations and the kinetics of CL vesicle fusion induced by these cations have been investigated. 31P-NMR measurements of equilibrium cation-CL complexes showed the lamellar-to-hexagonal (L α -H II) transition temperature ( T H) to be 20–25°C for the Sr 2+ and Ba 2+ complexes, whereas in the presence of Ca 2+ or Mg 2+ the T H was below 0°C. In the presence of Sr 2+ or Ba 2+, CL large unilamellar vesicles (LUVs) (0.1 μm diameter) showed kinetics of destabilization, as assessed by determination of the release of an aqueous fluorescent dye, which strongly correlated with the L α -H II transition of the final complex: at temperatures above the T H, fast and extensive leakage, mediated by vesicle-vesicle contact, was observed. On the other hand, mixing of vesicle contents was limited and of a highly transient nature. A different behavior was observed with Ca 2+ or Mg 2+: in the temperature range of 0–50°C, where the H II configuration is the thermodynamically favored phase, relatively nonleaky fusion of the vesicles occurred. Furthermore, with increasing temperature the rate and extent of leakage decreased, with a concomitant increase in fusion. Fluorescence measurements, involving incorporation of N-NBD-phosphatidylethanolamine in the vesicle bilayer, demonstrated a relative delay in the L α -H II phase transition of the CL vesicle system in the presence of Ca 2+. Freeze-fracture electron microscopy of CL LUV interaction products revealed the exclusive formation of H II tubes in the case of Sr 2+, whereas with Ca 2+ large fused vesicles next to H II tubes were seen. The extent of binding of Ca 2+ to CL in the lamellar phase, saturating at a binding ratio of 0.35 Ca 2+ per CL, was close to that observed for Sr 2+ and Ba 2+. It is concluded that CL LUVs in the presence of Ca 2+ undergo a transition that favors nonleaky fusion of the vesicles over rapid collapse into H II structures, despite the fact that the equilibrium Ca 2+-CL complex is in the H II phase. On the other hand, in the presence of Sr 2+ or Ba 2+ at temperatures above the T H of the respective cation-CL complexes, CL LUVs rapidly convert to H II structures with a concomitant loss of vesicular integrity. This suggests that the nature of the final cation-lipid complex does not primarily determine whether CL vesicles exposed to the cation will initially undergo a nonleaky fusion event or collapse into nonvesicular structures.

Binding properties of neuroligin 1 and neurexin 1beta reveal function as heterophilic cell adhesion molecules.

beta-Neurexins and neuroligins are plasma membrane proteins that are displayed on the neuronal cell surface. We have now investigated the interaction of neurexin 1beta with neuroligin 1 to evaluate their potential to function as heterophilic cell adhesion molecules. Using detergent-solubilized neuroligins and secreted neurexin 1beta-IgG fusion protein, we observed binding of these proteins to each other only in the presence of Ca2+ and in no other divalent cation tested. Only neurexin 1beta lacking an insert in splice site 4 bound neuroligins, whereas neurexin 1beta containing an insert was inactive. Half-maximal binding required 1-3 microM free Ca2+, which probably acts by binding to neuroligin 1 but not to neurexin 1beta. To determine if neurexin 1beta and neuroligin 1 can also interact with each other when present in a native membrane environment on the cell surface, we generated transfected cell lines expressing neuroligin 1 and neurexin 1beta. Upon mixing different cell populations, we found that cells aggregate only if cells expressing neurexin 1beta are mixed with cells expressing neuroligin 1. Aggregation was dependent on Ca2+ and was inhibited by the addition of soluble neurexin 1beta lacking an insert in splice site 4 but not by the addition of neurexin 1beta containing an insert in splice site 4. We conclude that neurexin 1beta and neuroligin 1 (and, by extension, other beta-neurexins and neuroligins) function as heterophilic cell adhesion molecules in a Ca2+-dependent reaction that is regulated by alternative splicing of beta-neurexins.

Fura‐2 signals evoked by kainate in leech glial cells in the presence of different divalent cations

The glutamate-agonist kainate evokes Ca2+ transients in both neurones and glial cells. Owing to the membrane depolarization elicited by kainate, a Ca2+ influx could occur through voltage-gated Ca2+ channels or through the kainate-gated cation channels directly. We have measured ratio signals of the calcium indicator dye fura-2, injected into giant glial cells of the leech Hirudo medicinalis, as response to kainate (5-20 microM) in the presence of different divalent cations. The responses to kainate increased during the first 2-4 kainate applications, both in unclamped and in voltage-clamped cells. The fura-2 fluorescence ratio (F350/F380) still increased when Ca2+ was replaced by Ba2+ but was suppressed in Ca(2+)-free saline and in the presence of Ni2+ (2 mM). Co2+ and Mn2+ (2 mM) also reduced the kainate-induced fura-2 fluorescence signals, due to entry of these divalent cations into the cells and subsequent quenching the fluorescence of the intracellular dye. It is concluded that Ni2+ blocks the kainate-induced membrane depolarization and Ca2+ transient but apparently does not enter the cells, while Ba2+, Co2+, and Mn2+ appear to permeate the membrane, presumably through the kainate-gated channels.

A Mn(2+)-enhanced, RGD-dependent adhesion technique for isolation of adult rat type II alveolar epithelial cells for immediate functional studies.

This report describes a Mn(2+)-enhanced, RGD-dependent adhesion technique for isolation of adult rat type II cells for immediate functional studies. Lung cells were dissociated by 30 U/ml porcine pancreatic elastase and 50 micrograms/ml trypsin instilled in the airways. Macrophages were selectively removed by adhesion on purified normal goat IgG-coated petri dishes. Type II cells were isolated by adhesion for 45 min, on ProNectin-F-coated dishes in the presence of 0.5 mM Mn2+. The adherent type II cells were then detached with 0.025% trypsin, 2 mM EDTA in Hepes-buffered saline, pH 7.4. The technique yielded 1.5 to 1.7 x 10(7) (n = 8) cells from a 150- to 200-g rat. Greater than 90% of the cells were pure type II cells as judged by tannic acid staining and immunostaining with monoclonal antibody 4AmAb, which recognizes pneumocin, a type II cell marker. The technique reduced the time required for cell isolation from the current 16 to 24 h to 2 to 2.5 h, using commonly available laboratory equipment and reagents. Cells isolated by the procedure were used to study cell adhesion and spreading on purified extracellular matrix components in the presence of different divalent cations. Mn2+, Co2+, Ni2+, and Mg2+ enhanced adhesion of freshly isolated type II cells to fibronectin and ProNectin-F, while Ca2+ did not promote type II cell adhesion on these substrata. RGDS peptide at 1 mg/ml concentration inhibited the divalent cation-enhanced cell adhesion.

Dnases of cell nuclei: Mn2+-dependent endonuclease

Comparison of catalytic properties of a Mn2(+)-dependent and a Ca2+, Mg2+ dependent endonucleases of rat liver cell nuclei was carried out. The Mn2(+)-dependent endonuclease has Mr 31 kDa by SDS-PAAG-electrophoresis; pH optimum 5.5; calcium-magnesium synergism less than 3 in rat liver DNA, RF M13 DNA and phage M13 DNA. The rate of hydrolysis of single strand and double strand circular DNA was the same. The Mn2(+)-dependent endonuclease split DNA by double hit manner, and didn't change the manner in the presence of different divalent cations. Ca2+, Mg2(+)-dependent endonuclease has pH optimum 6.5; calcium-magnesium synergism up to 40 in rat liver DNA and 175 in RF M13 DNA. The rate of hydrolysis of single strand DNA was higher than double-strand DNA.

Phosphorylation of Acid-soluble Proteins in Isolated Nucleoli of Novikoff Hepatoma Ascites Cells: EFFECTS OF DIVALENT CATIONS

Abstract Isolated nucleoli from rat Novikoff hepatoma ascites cells incorporated 32P of [γ-32P]ATP into acid-soluble nucleolar proteins in vitro in systems containing 0.25 m sucrose, 5 mm MgCl2, 12.5 mm NaCl, and 0.05 m Tris-HCl buffer (pH 7.3) at 37°. Although the total uptake of 32P reached a maximum after 15 min of incubation, the uptake into some protein bands increased with longer incubation times. As shown by two-dimensional gel electrophoresis and autoradiography, all the proteins labeled in vitro, including the high molecular weight proteins designated as C23-24, B27, and B13 were shown previously to be labeled in vivo (Olson, M. O. J., Orrick, L. R., Jones, C., and Busch, H. J. Biol. Chem. 249, 2823–2827). Divalent cations were necessary for phosphorylation in vitro but different profiles of phosphorylation were observed when Mg2+ was replaced with Co2+, Zn2+, or Mn2+. The presence of Zn2+ produced the highest 32P uptake associated with a marked increase in phosphorylation in proteins A17-19 and B23-25 compared to Mg2+ which produced high labeling in spots B13, and C23-24. These data indicate that the nucleolus contains phosphoprotein kinase(s) which exhibit different specificities in the presence of different divalent cations.

Circular dichroism studies on the conformation of transfer ribonucleic acid in the presence of different divalent cations.

Circular dichroism studies on the conformation of transfer ribonucleic acid in the presence of different divalent cations.

Conformation of carboxymethyl amylose in aqueous solutions

AbstractIntrinsic viscosity and specific optical rotation measurements have been carried out for Carboxymethyl amylose (CMA) solutions in 0.15M sodium chloride at various pH values. Potentiometric titrations of CMA have been performed at various polymer concentrations as well as in presence of different divalent cations. The amount of divalent cation (Ni+2) bound to CMA has been determined by using a new method af analysis based on polyelectrolyte theory. Finally from the results it is shown that CMA may exist as a random coil in solution.

On the role of metal cations in cellular adhesion: effect on cell surface charge.

AbstractAn examination has been made of the hypothesis that the role of divalent cations in promoting reaggregation of dissociated cells is principally to reduce the negative electrostatic charge at the cell surface. This hypothesis would suggest that cells in the presence of different divalent cations would reaggregate at identical rates if the concentrations of the different cations were so adjusted that in all cases the cells possess the same charge. This expectation has not been fulfilled. Magnesium ion was most effective in promoting reaggregation, calcium somewhat less so, and strontium and barium had little or no effect.