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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A spin labeling method for obtaining thermodynamic parameters of nucleotide association is proposed. The method is based on the dependence of ESR parameters of the spin-labelled derivative on concentration of the nonlabelled compound due to formation of associates involving both spin-labelled and unmodified molecules. It is found that at pH 7.5 the constant of adenylic nucleotide association practically does not depend on the number of phosphate groups and is equal to 9.7 +/- 0.3 M-1 for AMP, ADP and ATP in 0.1 M NaCl at 28 degrees C. In acidic medium the value of the association constant increases by a factor two. Base stacking is shown to make the main contribution to stability of the associates of adenylic nucleotides at neutral pH, whereas upon base protonation the key role is played, apparently, by base-phosphate interaction. It is thought, that an increase in the solvent entropy is essential for stabilisation of the associates, this factor being more important in the case of nucleotide association as compared to the association of nucleosides. A possible role of nucleotide association in the processes of intracellular regulation is discussed.
Mol Biol (Mosk)
PMID:[Study of intermolecular interactions and self-organization of adenylic nucleotides by the spin label method]. 624 47

The effect of Mg2+-ions on the physical state of thylakoid membrane and kinetics of electron transport between two photosystems were studied. The rate of electron transport from photosystem 2 to P700+ and the activity of photosystem 2 were obtained from the kinetics of P700 redox transients induced by flashes of white light (t1/2 = 7 musec or 0.75 msec) fired simultaneously with the background continuous far-red light (707 nm). The spin-labeled stearic acids (I1.14 and I12.3) were used as indicators of Mg2+-induced structural changes. Addition of MgCl2 stimulates incorporation of spin-labels into the lipid region of the thylakoid membrane. It was found that Mg2+-ions modify the ESR spectrum of I12.3. The results evidence that the screening of charged groups on the thylakoid membrane surface induces structural changes in the lipid region of the membrane. We have concluded that these structural changes result in reorientation of lipid molecules in the thylakoid membrane. There is a correlation between Mg2+-induced structural changes and electron transport in chloroplasts. Addition of Mg2+-ions stimulates the photochemical activity of photosystem 2 by increasing the amount of active reaction centres and modifies the rate constant of electron transport from photosystem 2 to P700+. It has been demonstrated that ion regulation of electron transport in more effective in the oxidising side than in the reducing side of plastoquinone shuttle.
Mol Biol (Mosk)
PMID:[Electron paramagnetic study of electron transport in photosynthetic systems. X. Effect of magnesium ions on the structural state of thylakoid membranes and the kinetics of electron transport between the two photosystems in bean chloroplasts]. 625 48

The dependence of the external and internal wide hyperfine extreme shifts of the ESR spectra on temperature and viscosity for spin-probes in solution of BSA was studied. Seven homologous spin-probes of carboline and benzocarboline derivatives were used. The obtained dependences are a consequence of the involvement of the spin-probe in two types of rotation: an anisotropic fast reorientation with tau > 10(-9) s with respect to a macromolecule and the isotropic one with tau > 10(-8) s due to rotation of the macromolecule itself. It was shown, that extrapolation values of a separation between hyperfine extreme do not reflect the degree of the immediate spin-probe environment polarity, but are determined by the hyperfine tenzor partial averaging as a result of the rapid anisotropic reorientation of the spin-probe. All spin-probes used were shown to be bound by the BSA molecule in the near vicinity of the tryptophan residue. The rotation correlation time of the BSA molecule was determined to be equal to 40 ns.
Mol Biol (Mosk)
PMID:[Study of binding of spin probes of the carboline and benzocarboline series to bovine serum albumin]. 625 16

Viscosity, temperature and ionic strength dependences of ESR microwave saturation parameters of spin labelled human oxyhemoglobin (Hb) and bovine serum albumin (BSA) have been studied. The piperidine and pyrrolidine nitroxyl derivatives of maleimide were used as covalent SH reagents for Hb and BSA and the same two derivatives of gamma-benzocarboline and spin labelled stearic acid were used as noncovalent spin probes for BSA. The effects of label binding tightness on ESR spectral parameters were considered. The rotational correlation times were determined using viscosity dependences of the separation of the outer hyperfine extrema and Stokes extrapolations at high viscosities. The ESR microwave saturation parameters of the spin labels were shown to depend just weakly on temperature (at constant eta/t) over the range 0-25 degrees and on g, A values but to be sensitive to protein rotational correlation times up to 10(-4) sec and also to the rotational anisotropy and to the relative motion of the spin label.
Mol Biol (Mosk) 1980
PMID:[Spin label study of slow molecular rotations of globular proteins using microwave saturation effects in electron paramagnetic resonance]. 626 31

The dependence of the ESR spectral parameters of spin labelled sarcoplasmic reticulum membranes on the amount of bound maleimide spin label is found which is shown to result from non-equivalence of the different SH groups rather than from enzyme activity changes on modification. Some structural characteristics (local polarity, the accessibility to water soluble reagents, the distance from ATP binding site) of the fast and slowly reacting SH groups were studied using selective labelling technique. The main contribution to the ESR absorption for both types of thiol groups gives the spin labelled Ca-ATPase. The slow rotational mobility of both types of strongly immobilized spin labels is measured using microwave saturation technique. This mobility is shown to be due essentially to intramolecular motion in different regions of the Ca-ATPase. The frequency of this motion correlates with the enzyme activity and it is sensitive also to the interaction of the enzyme with the substrates (ATP, acetylphosphate) and to the changes of lipid-protein interaction by temperature variation.
Mol Biol (Mosk)
PMID:[Study of Ca-dependent ATPase of sarcoplasmic reticulum by the use of selectively bound spin labels]. 626 63

The ESR spectrum of SO3- is observed directly during the oxidation of (bi)sulfite to sulfate by horseradish peroxidase. This radical exhibits a single line at g = 2.0031. The SO3-radical can be trapped with nitrosobenzene, yielding an ESR spectrum with coupling constants AN = 12.3 G,AHp = AHo = 2.4 G, and AHm = 0.9 G, and a g-value of 2.0053. SO3- is an intermediate in the two-step reduction of peroxidase Compound I by (bi)sulfite at physiological pH. At low pH, no SO3- is observed, which indicates a direct, one-step, two-electron reduction of Compound I. The pH at which the mechanism changes depends on the isoenzymes present. The radical reacts rapidly with oxygen as evidenced by the absence of an ESR spectrum when oxygen is present and by oxygen uptake measurements.
Mol Pharmacol 1982 Nov
PMID:Direct detection of the sulfur trioxide radical anion during the horseradish peroxidase-hydrogen peroxide oxidation of sulfite (aqueous sulfur dioxide). 629 62

p-Aminophenol oxidation is catalyzed by horseradish peroxidase. ESR spectroscopy demonstrates the formation of the p-aminophenoxy free radical, the one-electron oxidation product of p-aminophenol. The same radical is formed by alkaline autoxidation of this compound. The ultimate products of p-aminophenol oxidation are mainly polymeric; however, indophenol was isolated in low yield. Oxidation of p-aminophenol is also catalyzed by the hydroperoxidase activity of prostaglandin synthase, using ram seminal microsomal preparations as the enzyme source.
Mol Pharmacol 1983 Mar
PMID:Oxidation of p-aminophenol catalyzed by horseradish peroxidase and prostaglandin synthase. 630 Jun 52

A spectral division method of two conformational states of spin-labeled macromolecules is presented. The method is suitable in conditions of highly anisotropic motion of spin label and is based on titration of experimental spectra of spin-labeled macromolecule by theoretical ones. Theoretical spectra simulation uses the Freed theory and spin-Hamiltonian parameters, derived from independent experiments. Nomogrammes and formula for calculation of order parameter Sz and correlation time tau c in temperature-viscosity experiment are available. The method was applied to spectral division of two conformational states of spin-labeled tRNAPhe from E. coli and spectral parameters Sz and tau c were obtained for both states. ESR spectra of these conformational states at t degree = 20 degrees differ strongly from one another by order parameter Sz. The first conformer, that is characterised by a greater order parameter has no globular conformational transition (in terms of changes of the hydrodynamic macromolecule radius) between 2 degrees and 20 degrees, but local conformational changes take place in this temperature region.
Mol Biol (Mosk)
PMID:[Spectral division of conformational states of spin-labeled tRNA Phe from Escherichia coli]. 630 93

The hydrophobic spin label used in ESR showed that the iminoxyl radical rotation in the native membrane of sarcoplasmatic reticulum (SR) occurred much faster than in the membranes, modified by a synthetic lipid. Such effect was observed throughout the whole temperature range (7-40 degrees). Experimental technique for the modification of the SR membrane and the lipid by ultrasonic treatment has been developed. Synthetic lipids without ultrasonic treatment did not inhibit the activity of Ca2+-ATPase. The change in both the enzyme activity and its ability to transport the Ca2+ ions through the membrane vesicules was observed after the phospholipids incorporation into the SR membrane. The investigation of the temperature dependence (in Arrhenius coordinates) of native and modified by lecithin Ca2+-ATPase after ultrasonic treatment and also of a "pure enzyme" showed the presence of two sharp breaks at 20 degrees and 40-42 degrees. It was shown tha the break of an Arrhenius anamorphosis was caused by a lipid environment of ATPase, "melting" of a phospholipid bilayer. The break at 20-22 degrees was observed in all cases and even after the incorporation of all the lipids into the SR membrane. This phenomenon can be explained by the distortion of the protein-lipid interaction, affecting the conformation mobility of protein and the geometry of its catalytically active center.
Mol Biol (Mosk)
PMID:[Incorporation of synthetic phospholipids into the membranes of the sarcoplasmic reticulum from the rabbit muscle]. 630 94

ESR spectra of erythrocyte membranes labeled with a maleimide spin label (MSL) show two types of label environment: a weakly immobilized component and a strongly immobilized component. Chlorpromazine (CPZ) markedly altered the spectra: at pH 8.0, 3 mM CPZ reduced the amplitude of the spectrum by 40%, and the weakly immobilized component was almost completely removed. In order to clarify the mechanisms of these spectral changes the protein release from erythrocyte membranes induced by CPZ has been followed. CPZ had a weak solubilizing effect on erythrocyte membranes: less than 1% of the membrane protein was released, mainly Band 6. By comparison with the protein release induced by low-salt treatment it was found that the "detergent-like" property of CPZ cannot explain the alterations in the ESR spectra. The nature of the spectral changes induced by CPZ was different from that of changes induced by lowering the pH to 4.5; correlated with other data this shows that changes in organization or conformation of membrane protein cannot explain the CPZ-induced alterations in the ESR spectra. These spectral changes appeared to be due to the reduction by CPZ of the nitroxide free radical. This was documented by the marked reduction of spin concentration of the labeled ghosts in the presence of CPZ resulting in a decrease in amplitude of the ESR spectrum of MSL-labeled erythrocyte ghosts induced by CPZ. The reduction by CPZ of the nitroxide free radical was compared with that induced by ascorbate. It was found that CPZ preferentially reduces the mobile component of the ESR spectrum of MSL-labeled ghosts. The action of CPZ in reducing free radicals may have consequences for patients receiving long-term treatment with phenothiazine derivatives.
Mol Pharmacol 1983 May
PMID:Effect of chlorpromazine on proteins in human erythrocyte membranes as inferred from spin labeling and biochemical analyses. 630 35


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