Salt ion interaction with the protein molecule: the facts and the concept

The effect of salt concentration and its nature on some properties of alpha-chymotrypsin (the catalytic activity, the solution optical density, the sedimentation coefficient) has been considered. The limiting stage of enzyme-salt interaction has been shown to change with the variation of experimental conditions. As salt concentration increases the surface electrostatic interaction of salt ions with the enzyme molecule changes by ions penetration via certain channels within the protein globule and their subsequent binding to regulatory centers. The difference in ions nature and binding centers provides the variety of modifications observed. At high salt concentrations the solvent structure becomes predominant.     

The effect of binding divalent metal ions on the conformation of human angiotensin-II in solution as probed by nuclear and electron paramagnetic resonance investigations

The interaction between human angiotensin-II and Mn(II) ions in water solution has been deline-ated by nmr and esr experiments. A pH-dependent binding interaction with the imidazole moiety of His 6 has been shown, ratifying the suggestion that His 6 is involved in intramolecular structuring within the peptide molecule.     

Synthetic and binding studies on the calcium binding site I of bovine brain calmodulin. II. Synthesis and CD studies on the cyclic 20-31 sequence

The synthesis of the cyclic 20-31 sequence of bovine brain calmodulin corresponding to the loop of the hypothetical calcium binding site I of the protein has been accomplished by classical solution methods. The interaction of the synthetic cyclic fragment with calcium ions has been investigated by CD spectroscopy in water and in 98% trifluoroethanol solution. Calcium ions have no effect on the dichroic absorption of aqueous solution of the cyclic dodecapeptide in the wavelength range 200-250 nm. In 98% trifluoroethanol the CD spectrum of the cyclic compound in the absence of calcium ions is almost identical to that of the linear dodecapeptide in the presence of saturation concentrations of calcium. This result supports our previous hypothesis of a folding of the linear sequence upon interaction with the metal ion. The cyclic peptide also interacts with calcium ions in 98% trifluoroethanol forming a 1:1 complex.     

Effect of calcium ions on potassium conductivity of latrotoxin channels

It has been shown that inhibition of potassium current through latrotoxin channels by calcium ions is followed by electrostatic interaction of these ions with a total charge on the mouth of the channel.     

Mechanism of the inhibition of milk xanthine oxidase activity by metal ions: a transient kinetic study

The nature and mechanism of the inhibition of the oxidoreductase activity of milk xanthine oxidase (XO) by Cu(2+), Hg(2+) and Ag(+) ions has been studied by steady state and stopped flow transient kinetic measurements. The results show that the nature of the inhibition is noncompetitive. The inhibition constants for Cu(2+) and Hg(2+) are in the micromolar and that for Ag(+) is in the nanomolar range. This suggests that the metal ions have strong affinity towards XO. pH dependence studies of the inhibition indicate that at least two ionisable groups of XO are involved in the binding of these metal ions. The effect of the interaction of the metal ions on the reductive and oxidative half reactions of XO has been investigated, and it is observed that the kinetic parameters of the reductive half reaction are not affected by these metal ions. However, the interaction of these metal ions with XO significantly affects the kinetic parameters of the oxidative half reaction. It is suggested that this may be the main cause for the inhibition of XO activity by the metal ions.     

Calcium-activated membrane interaction of the islet amyloid polypeptide: implications in the pathogenesis of type II diabetes mellitus

The role played by Ca²⁺ ions in the interaction of the human islet amyloid polypeptide (hIAPP) with model membranes has been investigated by differential scanning calorimetry (DSC) and circular dichroism (CD) experiments. In particular, the interaction of hIAPP and its rat isoform (rIAPP) with zwitterionic dipalmitoyl-phosphatidylcholine (DPPC), negatively charged dipalmitoyl-phosphatidylserine (DPPS) vesicles and with a 3:1 mixtures of them, has been studied in the presence of Ca²⁺ ions. The experiments have evidenced that amorphous, soluble hIAPP assemblies interact with the hydrophobic core of DPPC bilayers. Conversely, the presence of Ca²⁺ ions is necessary to activate a preferential interaction of hIAPP with the hydrophobic core of DPPS membranes. These findings support the hypothesis that an impaired cellular homeostasis of Ca²⁺ ions may promote the insertion of hIAPP into the hydrophobic core of carrier vesicles which is thought to contribute to an eventual intracellular accumulation of β-sheet rich hIAPP aggregates.     

NADPH-Induced Microsomal Lipid Peroxidation as Measured by Malondialdehyde Production in Rat Liver. Inhibitory Effect of Naftidrofuryl

The effects of naftidrofuryl have been studied on NADPH-induced microsomal lipid peroxidation by measuring malondialdehyde (MDA) production. Conditions adequate to measure MDA production and effects of naftidrofuryl on MDA production have been tested. It has been shown that the addition of ferric ions is essential with Tris or Pipes buffers while it can be omitted with phosphate known to contain traces of ferric ions. However the initial rate of MDA production is much lower with phosphate in the absence of added ferric ions, showing that the initiation of lipid peroxidation is limited by ferric ions. The effects of naftidrofuryl have been studied on MDA production in phosphate buffer in the presence or absence of ferric ions. Naftidrofuryl inhibits lipid peroxidation in both conditions indicating that the inhibition is not related to an interaction with added ferric ions. Naftidrofuryl is efficient at concentrations slighty higher than butylhydroxytoluene but lower than aminopyrine.     

Spin-label studies on the specificity of interaction of cardiolipin with beef heart cytochrome oxidase

The selectivity of interaction of various cardiolipin analogues with beef heart cytochrome oxidase in reconstituted complexes with dimyristoylphosphatidylcholine has been studied by electron spin resonance spectroscopy, using lipids spin-labeled in the acyl chains. No difference in selectivity is observed between cardiolipin and its monolyso derivative, and similarly no selectivity is observed between phosphatidylcholine and lysophosphatidylcholine. Removal of the cardiolipin charge by methylation of the phosphate groups reduces but does not eliminate selectivity relative to phosphatidylcholine. The dependence of the lipid selectivity on head group and chain composition is in the order cardiolipin approximately equal to monolysocardiolipin greater than acylcardiolipin greater than dimethylcardiolipin greater than phosphatidylcholine approximately equal to lysophosphatidylcholine, where acylcardiolipin has the spin-label chain attached at the center -OH of the head group. The degree of association of the negatively charged cardiolipin derivatives with cytochrome oxidase decreases with increasing salt concentration, to a level comparable to that for dimethylcardiolipin. At high ionic strength there is still a marked selectivity relative to phosphatidylcholine. Li+ ions are more effective in screening the interaction than are Na+ ions, and divalent ions are more effective than monovalent ions. The selectivity for cardiolipin is only slightly reduced on titrating the protein to high pH. Alkylation of the protein with N-ethylmaleimide has little effect on the titration behavior. Covalent modification of the protein by reaction with citraconic anhydride decreases the selectivity of interaction with cardiolipin. It is concluded that cardiolipin possesses an additional specificity of interaction with cytochrome oxidase other than that of purely electrostatic origin.     

Synthesis and physicochemical characterization of Gd-DTPA-B(sLex)A, a new MRI contrast agent targeted to inflammation

A new magnetic resonance imaging (MRI) contrast agent designed to mimic sialyl Lewis X (sLeX) and to target inflammation has been synthesized and characterized. The evolution of its proton longitudinal relaxivity as a function of the magnetic field (NMRD) and temperature has been studied. The exchange rate of the water coordinated to the metal has been assessed by oxygen-17 relaxometry. The transmetalation by zinc(II) ions and the noncovalent binding to human serum albumin have been evaluated. The results show no limitation by the residence time of the coordinated water molecule above room temperature, a higher stability of the complex versus transmetalation by zinc(II) ions than a parent complex, the clinically used Gd-DTPA-BMA, and negligible interaction with human serum albumin.     

Energy of ion pairs in proteins

The energy of ions interaction in an ionic pair and the energy of ions transfer from water into protein at different ions disposition relative to the protein/water boundary has been considered. Ultimately, the ions transfer from aqueous phase into protein, i. e. in the medium with a low dielectric constant is energetically unfavorable and hence it cannot stabilize the protein structure by itself. For stabilization of ionic pairs in protein the action of some additional factors is necessary, in particular the action of the intraglobular electric field.     

Effect of complex formation by taxifolin and naringenin with Cu(i) ions on the distribution of the components of complexes in the octanol–water system

The interaction of two structurally close flavanones: taxifolin and naringenin with copper(I) ions and its effect on the distribution of flavonoids and the corresponding ions in a biphasic system octanol–water have been studied. It has been shown that these polyphenols form complexes with copper ions of different stoichiometric ratio depending on the pH of medium (5.4, 7.4, and 9.0). The interaction of the flavonoids with copper ions leads to an increase in the fraction of polyphenols in the water phase at all pH values examined. The fraction of metal ions in octanol in the presence of both taxifolin and naringenin is maximal in the range of neutral pH values. The parameters obtained in the study, such as the partition coefficient and the coefficient of distribution in a biphasic system octanol–water (logP and logD) form the physicochemical basis necessary for the estimation of the bioavailability of flavonoids and the corresponding metal ions upon their combined consumption.     

温度和时间对肌红蛋白血红素铁与金属离子相互作用的影响

目的:研究在生理条件下,温度和时间对肌红蛋白血红素铁与各种金属离子直接相互作用的影响。方法:利用紫外-可见光谱法研究肌红蛋白活性中心的铁和外加金属离子(CuSO4、ZnSO4、MgSO4、CoCl2和MnSO4)的直接相互作用;改变作用温度(4、21、37和52℃)和作用时间(2、4、6、8和10 d),研究肌红蛋白活性中心铁卟啉与不同金属离子的直接相互作用。结果与结论:紫外光谱数据表明,金属离子与肌红蛋白活性中心的Fe(Ⅱ)发生直接相互作用,且随着作用温度的升高和作用时间的延长,这种相互作用逐渐增强。作用10 d后,金属离子与肌红蛋白活性中心的铁的作用强度依次为Mn(Ⅱ)>Zn(Ⅱ)>Co(Ⅱ);温度升至52℃时,作用强度依次为Cu(Ⅱ)>Mg(Ⅱ)>Zn(Ⅱ)。     

A laser Raman spectroscopic study of the interaction of calf-thymus DNA with Cu(II) and Pb(II) ions: metal ion binding and DNA conformational changes.

The interaction of calf-thymus DNA with Cu(II) and Pb(II) ions has been investigated in H2O and D2O solutions at physiological pH, using laser Raman spectroscopy. The results confirm the destabilizing effect of Cu2+ ions, which are shown to bind strongly to the guanine and cytidine bases, perturbing the A-T base pairs and disrupting the double-helical structure of DNA, whose conformation is markedly altered by these interactions. Earlier claims that Pb2+ ions destabilize DNA are not supported by the present study. These ions are found to interact only weakly with the nucleic bases, binding to the N7 position of the guanine bases and also interacting with the A-T pairs. Both types of ions are found to interact with the charged phosphate groups of DNA, although these sites are preferred over the nucleic bases by Pb2+ ions.     

Calcium-dioxolene complexes: rate constants of pyrocatechol oxidation in the presence of Ca2+

The effect of calcium ions on the rate of pyrocatechol autoxidation at pH 9.0 has been studied by mathematical modeling. The effect of Ca2+ on the oxygen absorption rate has been studied, and a kinetic model has been suggested, which takes different stages of interaction of pyrocatechol and its radical form with oxygen into account. It has been shown that the prooxidant action of Ca2+ is related to an abrupt increase (approximately by three orders of magnitude) in the rate constant of comproportionation (reaction of chain branching and formation of o-semiquinonates) and a marked decrease (by two orders of magnitude, from 1.4 10(7) to 0.6 10(5) M(-1)s(-1)) in the rate constant of disproportionation of o-semiquinones. The system can be used as a model for studying the prooxidant action of calcium ions.     

Interaction of mithramycin with metal ions and DNA

The interaction of mithramycin with metal ions has been studied by absorbance and fluorescence spectroscopy. Magnesium shifts the drug absorbance spectrum to longer wavelengths and displays a weak binding constant (Kd = 1mM); no interaction with calcium was detected. The drug requires magnesium for binding to DNA and this is characterised by small additional hypochromic and bathochromic changes. Mithramycin does not bind to DNA in the presence of calcium. With 10mM magnesium the drug binds to DNA with an association constant of 9.2 x 10(4) M-1. The inability of calcium to substitute for magnesium has been confirmed by 'footprinting' experiments using both DNase I and hydroxyl radicals.     

Prion metal interaction: Is prion pathogenesis a cause or a consequence of metal imbalance?

Functional role of cellular prion protein (PrPc) has been hypothesized to be in metal homeostasis and providing cells with a superoxide dismutase (SOD)-like activity to escape damage by reactive oxygen species (ROS). PrPc interacts with a range of divalent metal ions and undergoes Cu²⁺ as well as Zn²⁺-associated endocytosis, thereby maintaining homeostasis of these and other metal ions. Conformational change to a β-sheet rich, protease resistant entity, reminiscent of the disease-associated scrapie form called PrPsc, has been found to be induced by interaction of PrPc with metal ions like Cu²⁺, Zn²⁺, Mn²⁺ and Fe²⁺. This review compiles data from various experimental studies of the interaction of metals with PrPc. The effect of metal ions on the expression and conformation of the prion protein is described in detail with emphasis on their possible physiological and pathogenic role. Further, a hypothesis is presented where attainment of altered conformation by metal-bound PrPc has been viewed as a deleterious consequence of efforts made by cells to maintain metal homeostasis. Thus, PrPc presumably sacrifices itself by converting into PrPsc form in an attempt to protect cells from the toxicity of metal imbalance. Finally, possible reasons for contradictions reported in the literature on the subject are explored and experimental approaches to resolve the same are suggested.     

Zinc-induced interactions of the metal-binding domain of beta-amyloid with nucleic acids and glycosaminoglycans

Zinc ions form complexes with β-amyloid peptides and play an important role in Alzheimer’s disease pathogenesis. It has been demonstrated by turbidimetry and correlation spectroscopy that synthetic peptide Aβ16 representing the metal-binding domain of β-amyloid is able to interact with nucleic acids, chondroitin polysulfate, and dextran sulfates in the presence of zinc ions. The amino acid D7H substitution enhanced the peptide binding to polyanions, whereas the H6R and H6A-H13A substitutions abolished this interaction. It is suggested that the metal-binding domain may serve as a zinc-dependent site of β-amyloid interaction with biological polyanions including DNA, RNA, and glycosaminoglycans.     

Interaction of deoxyguanylic acid with alkaline earth metal ions. Evidence for the deoxyribose C3'-endo/anti, O4'-endo/anti and C2'-endo/anti conformational transitions

The interaction of 2'-deoxyguanosine-5'-monophosphoric acid (H2-dGMP) with the alkaline earth metal ions has been investigated in aqueous solution at neutral pH. The solid salts of the type Mg-dGMP.5H2O Ca-dGMP.6H2O, Sr-dGMP.7H2O and Ba-dGMP.7H2O were isolated and characterized by FT-IR, proton-NMR and X-ray powder diffraction measurements. Two types of metal-nucleotide interactions have been identified: (a) the indirect metal-base and the direct metal-phosphate bindings (outer- and inner-sphere interaction), for the Mg(II) and Sr(II) ions and (b) the direct metal-base and direct metal-phosphate bindings (inner-sphere interaction), for the Ca(II) and Ba(II) ions. In aqueous solution, a dynamic equilibrium of the type base-metal-H2O. . .PO3 in equilibrium base. . .H2O-metal-PO3 is present. The deoxyribose moiety exhibits C3'-endo/anti conformation, in the Mg(II)-, Ca(II)-, Sr(II)- and Ba(II)-dGMP salts.     

Conformation and calcium binding properties of gastrin fragments of increasing chain length

Conformation and calcium binding properties of a series of gastrin-related peptides, in which the glutamic acid sequence at the N-terminal portion of the molecule has been elongated step by step, have been investigated using circular dichroism spectroscopy. A working hypothesis about the structure of these hormones in trifluoroethanol has been proposed. The structure comprises aβ-bend located at the level of the sequence Ala-Tyr-Gly-Trp. A correlation between chain elongation and increase of biological potency has been observed. All examined peptides strongly interact with calcium ions in trifluoroethanol. The variation of the circular dichroism spectra upon calcium addition provided some information about the groups involved in the coordination of the ions. Our results allow the hypothesis of the presence of one binding site, located at the C-terminal portion of the molecule in the gastrin octapeptide, and of an additional site at the N-terminus, in the longer fragments. The carboxyl function of Asp and Glu side-chains, at the two ends of the molecules, are probably involved in the interaction with the metal ions.     

Simulations of the bis-penicillamine enkephalin in sodium chloride solution: a parameter study.

A simulation study of DPDPE in sodium chloride solution has been performed and compared with previous simulations using a different interaction potential for the ions. Both global thermodynamics as well as a characterization of association to DPDPE have been calculated. We show that the parameters used for the ions have a profound effect on the association to the peptide in 1M NaCl. The observed differences suggest that individual associations in these and previous simulations are sensitive to parameters.