Ion-dependent Changes Research Articles

Vibrational Relaxation in EDTA Is Ion-Dependent.

Ion binding by carboxylate groups is common in biomolecules such as metalloproteins, but dynamical aspects of ion binding are not fully understood. We present ultrafast spectroscopic measurements of vibrational relaxation in the ion-coordinating carboxylate groups of EDTA, which we use as a model of carboxylate-mediated ion binding, as EDTA binds a series of divalent and trivalent metal ions with high affinity. The measurements are interpreted using a Redfield-based anharmonic model of vibrational relaxation that rationalizes trends in vibrational lifetimes in terms of vibrational energy transfer between EDTA's asymmetric carboxylate stretching vibrational modes and lower-lying modes. Results show ion-dependent changes in complex structure and dynamics well outside the temporal and spatial resolution of common structural methods and demonstrate how vibrational relaxation measurements may contribute to exploration of ion-binding dynamics on ultrashort length and time scales.

Mössbauer studies of the effect of swift heavy ion irradiation on electrodeposited Sn-Co-Fe coatings

57Fe and 119Sn conversion electron Mössbauer spectroscopy was used to study the radiation effect of 246 MeV Kr and 710 MeV Bi ions on electrochemically deposited amorphous Sn-Co-Fe coatings. The ion dependent changes induced by the swift heavy ion irradiation in the chemical short range order of these amorphous thin films regarding Fe and Sn atoms are discussed within the framework of the transient thermal spike model.

Novel Ca 2+-selective merocyanine-type chromoionophore derived from calix[4]arene-diamide

The synthesis and calcium-selective chromogenic ion binding properties of benzothiazolium derivative of calix[4]arene are described. The merocyanine-type ionophore derived from calix[4]arene-diamide showed selective chromogenic properties toward Ca 2+ ions in aqueous methanol. The compound showed significant Ca 2+ ion dependent changes in UV–vis spectral properties in the presence of other physiologically important metal ions (Na +, K +, and Mg 2+). The pH sensitive chromogenic behavior also suggests that the compound can be used as a sensitive pH indicator around pH 6.5.

Structure of the Trinucleotide D-acp3U-A with Coordinated Mg2+Demonstrates that Modified Nucleosides Contribute to Regional Conformations of RNA

Abstract In tRNA crystal structures, the only nonaromatic ribonucleoside, dihydrouridine (D) and 3′-adjacent nucleotides adopt the infrequent 2′-endo conformation. Analysis of D, DUA and UUA by circular dichroism (CD) and NMR confirmed that D produces the 2′-endo conformation of the trimer and is responsible for the same in tRNA. The nucleoside, 3-[3-(S)-amino-3-carboxypropyl]uridine (acp3U) occurs in the tRNA sequence D-acp3U-A. CD spectra indicated that D-acp3U-A and U-acp3U-A bind Mg2+, whereas acp3U, D-acp3U, DUA and UUA do not. Ion dependent changes in chemical shifts and paramagnetic broadening of 1H signals indicated that Mg2+ coordination involved the acp3U side chain and the ribose of A. The Mg2+-bound structure was modeled with simulated annealing, molecular mechanics and NMR restraints. Acp3U contributed to local charge density that facilitated Mg2+ coordination. #Present addresses: W. W. S., NMR Facility University of California, Davis, CA; B. F., School of Medicine, University of North Caroli...

Binding of histones H1 and H5 and their globular domains to four-way junction DNA.

We have compared chicken erythrocyte linker histones H1 and H5 binding to a synthetic four-way DNA junction. Each histone binds to form a single complex, with an affinity which permits competition against a large excess of linear duplex DNA. The affinity of H5 is higher than that of H1. The globular domain from either protein will also bind strongly, but in this case multiple binding occurs. Binding of intact H1 is inhibited by cations: Mg2+ and spermidine are very effective, Na+ much less so. This inhibition is not likely to be a general ion-competition effect, for Mg2+ is much less effective in inhibiting the binding of H1 to linear DNA. Instead, the inhibition of binding may be due to ion-dependent changes in the conformation of the four-way junction, which are known to occur under similar conditions. These results strongly suggest that the angle formed between the arms of the DNA junction could be a major determinant in the interaction of H1 with DNA crossovers.

Sodium-independent, hydrogen ion-dependent changes in membrane potential and conductance induced by dipeptides in Triturus enterocytes.

The effects of Na+ and pH in the medium on dipeptide transport across Triturus small intestinal brush border membrane were studied electrophysiologically. Although glycylglycine exists mainly in the zwitterionic form at pH 7.30, it induced marked depolarization in the membrane potential and reduction in the input resistance both in the presence and absence of Na+ in the medium. Similar Na+-independent depolarization and resistance change were also observed with L-carnosine. On the contrary, glycine induced membrane depolarization and reduction in the input resistance only in the presence of Na+ in the medium. When pH of the medium was lowered to 6.00, the magnitude of the depolarization induced by glycylglycine increased by 33%, while at pH 8.30, it decreased by 39%. These data indicate that dipeptide transport across the intestinal brush border membrane is coupled with H+ and has no direct interaction with Na+.

Low frequency pulsed magnetic fields do not modify several aspects of ion transport in biological materials

Pulsed magnetic fields (P.M.F.s) are widely used to promote fracture repair in delayed unions of bone, yet it is not clear how they interact with biological materials. It has been proposed that induced currents impinging on cell membranes may contribute to their ion transport function, leading to ion-dependent changes in metabolism. This hypothesis was tested by treating in vitro models for ion transport processes with short-term exposure to P.M.F.s. No change occurred in active transport of potassium or calcium in human red cells, or calcium transport through an epithelial membrane, nor were passive movements of ions altered by P.M.F.s. An indirect mechanism was considered: connective tissue matrices sequester ions according to their Donnan potential. The electric fields associated with spatial variation in Donnan potential are small, so that pulsed magnetic fields might interact with them and displace ions from the matrix, hence modifying ion transport in connective tissue cells. Results showed, however, that calcium accumulation in cartilage matrices was insensitive to P.M.F.s. From these studies it seems unlikely, therefore, that modification of cellular ion transport is the initial interaction between pulsed magnetic fields and biological materials.

Sodium and potassium ion-dependent change in oligomerization of Na,K-ATPase in C12E8 detected by low-angle laser light scattering technique in combination with high performance porous silica-gel chromatography.

Approximate molecular weights and the subunit structures of Na,K-ATPase from horse kidney were estimated by means of the combination of porous silica gel chromatography, laser light scattering (LS) and refractive index (RI) measurements in C12E8. When the enzymes were eluted with NaCl- or KCl-containing solution, 3 or 4 protein peaks, respectively were detected except that of low molecular weight range. These peaks were tentatively named Na-1, Na-2, Na-2', Na-3 (NaCl-containing eluents), K-1, K-2, K-3 (KCl-containing eluents), respectively. Na,K-ATPase and K-p-nitrophenylphosphatase activities were detected at all peaks. The activities were completely inhibited by ouabain. The ratios of the output from laser light scattering to that of differential refractive index intensity for reference proteins and these peaks were compared. Relative values of refractive index increments of BSA, thyroglobulin and C12E8 measured with the same RI detector under the same conditions were 0.144, 0.141, and 0.135 respectively. The size of the enzyme at the main peak (K-2) with K eluents (KCl 10 mM, 25 mM) was twice that at the main peak (Na-2') with Na eluents (1, 25, 50 mM NaCl) assuming that dn/dc of K-2 is similar to that of Na-2'. Na-3 and K-3 appeared at the same retention time and showed the same values of LS/RI. Provided that the dn/dc values of both peaks are similar to those of Na-2' and K-2, the sizes of Na-3 and K-3 are one-third of Na-2' and one-sixth of K-2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical modification analysis of ion-dependent changes in the solution structure of yeast phenylalanine tRNA

Chemical modification analysis of ion-dependent changes in the solution structure of yeast phenylalanine tRNA

Does calcium ion binding control plant virus disassembly?

Hydrogen ion titration data on brome mosaic, turnip crinkle, and turnip yellow mosaic viruses in the presence and absence of calcium ions are presented and analyzed. Published evidence on pH- and divalent ion-dependent changes in other viruses is reviewed in the light of current knowledge about cation-binding sites. It appears that most, perhaps all, plant viruses contain calcium-binding sites with some of the properties to be expected for a switch controlling disassembly. Practical conclusions follow for virus purification and reassembly experiments.

Purification and some morphological characters of wheat striate mosaic virus

Hydrogen ion titration data on brome mosaic, turnip crinkle, and turnip yellow mosaic viruses in the presence and absence of calcium ions are presented and analyzed. Published evidence on pH- and divalent ion-dependent changes in other viruses is reviewed in the light of current knowledge about cation-binding sites. It appears that most, perhaps all, plant viruses contain calcium-binding sites with some of the properties to be expected for a switch controlling disassembly. Practical conclusions follow for virus purification and reassembly experiments.