Showing papers on "Conformational change published in 1973"
391 citations
TL;DR: The dicoumarol-induced prothrombin had only one high affinity binding site and no ligand-induced conformational change was detected in this prothromabin.
125 citations
TL;DR: Preliminary evidence suggests that these subunits of bovine adrenal medulla 3,4-dihydroxyphenylethylamine β-hydroxylase are identical, and the binding of anions to a basic group adjacent to the ionizable group at the active site has been proposed to explain the mechanism of activation by these compounds.
114 citations
TL;DR: It was concluded from this series of experiments that removal ofretinol from retinol-binding protein results in a conformational change such as to make apo-RBP unable to bind to prealbumin.
89 citations
TL;DR: The remarkable differences in the stabilities of the various cation complexes of depsipeptide antibiotics bound to lecithin vesicles as well as in homogeneous solution were related to different conformations of the ligands in these complexes as characterized by spectroscopic techniques.
Abstract: Conformational rearrangements of membrane-active peptide and depsipeptide antibiotics such as enniatin B, valinomycin, and valine-gramicidin A have been studied as a function of solvent polarity employing ultrasonic absorption methods. The results provide information about the number of occupied conformational states and their respective rates of interconversion. The interpretation of the results from kinetic measurements was confirmed by spectroscopic studies.
The remarkable differences in the stabilities of the various cation complexes of depsipeptide antibiotics bound to lecithin vesicles as well as in homogeneous solution were related to different conformations of the ligands in these complexes as characterized by spectroscopic techniques. Kinetic studies by relaxation methods led to the elucidation of the mechanism of complex formation. Complexation of cations follows a multistep reaction. For valinomycin the rate-limiting step of cation complexation is a ligand conformational change which occurs during the stepwise substitution of solvent molecules from the cation.
67 citations
TL;DR: The results indicate that increase in concentration or decrease in temperature and in the ionization of carboxyl group promotes the formation of ordered cross-link regions.
57 citations
TL;DR: The results suggest that the activation by Mg2+ proceeds through a binding of the metal with free enzyme which might be followed by a conformational change, rather than by an action on the substrate.
56 citations
TL;DR: Circular dichroism, optical rotatory dispersion, and absorption studies allowed direct observation of the functioning enzyme protein and confirmed the major transformations of rhodanese indicated by study of the thermodynamic parameters.
52 citations
TL;DR: Superimposed spectra for a given agent have isoslopic points and suggest that solubilization with a particular agent may be a two-state process.
49 citations
TL;DR: Binding of glucose-6- P induces conformational change in rat brain hexokinase (ATP: d -hexose 6-phosphotransferase, EC 2.7.1) as indicated by decreased susceptibility to digestion by chymotrypsin and an increased sedimentation coefficient on sucrose density gradients.
42 citations
TL;DR: A mechanical model for the operation of the regulatory mechanism in the anthraniate aggregate is presented and it is clear that the equilibrium between active and inhibited conformational states of the aggregate is susceptible to mutational alteration.
TL;DR: It is shown that e-prototoxin and e-toxin possess high amounts of β-conformation, and the activation of e-Prototoxin is accompanied by a conformational change since significant differences were observed in the ORD and CD parameters.
TL;DR: Spin-labeling with 7 and 12-nitroxide-labeled stearic acids and high and low-angle X-ray diffraction provide strong evidence that the phospholipid in the purified (sodium + potassium)-activated adenosinetriphosphatase from the rectal gland of Squalus acanthias possesses bilayer character as mentioned in this paper.
TL;DR: In this paper, the effect of sodium octyl, decyl, and dodecyl sulfates on the circular dichroism (CD) of Bence-Jones protein, concanavalin A, soybean trypsin inhibitor, and trypsins was investigated The concentrations of the detergents were varied and the minimal amounts were determined that affect the conformation
TL;DR: The change in surface tension of solutions of poly‐L‐lysine in water has been studied as a function of temperature at various pH values and changes at various temperatures have been correlated with changes in the circular dichroic spectra reflecting conformational change.
Abstract: The change in surface tension of solutions of poly-L-lysine in water has been studied as a function of temperature at various pH values. The changes at various temperatures have been correlated with changes in the circular dichroic spectra reflecting conformational change. In addition to the major transition at 50°C attributed to the conversion of the α-helical β conformation, two other transitions have been observed at 30°C and 80°C.
A minimum in the surface tension value was observed at pH 10, near the pK value for poly-L-lysine. It was concluded that at this pH the concentration of hydrophobic groups at the surface was a maximum.
TL;DR: It is inferred that a quaternary enzyme-pyruvate-NO(3) (-)-MgADP complex could form, but no evidence was obtained to suggest that it possessed special properties comparable with those found with creatine kinase, and the implications for the unidirectional nature of the mechanism of pyruVate kinase are discussed.
Abstract: 1. An improved purification procedure for the brain-type creatine kinase from ox smooth muscle is described. 2. Michaelis constants show the characteristic dependence on the concentration of the second substrate: the derived constants are compared with those for the enzyme from ox brain. 3. Inhibition by iodoacetamide gives a biphasic curve and the total extent of the reaction depends on the enzyme concentration. The rate of inhibition at pH8.6 is not affected by creatine plus MgADP or by a range of simple anions. Addition of creatine plus MgADP plus either NO(3) (-) or Cl(-) ions affords 71.5 and 44% protection respectively. ADP could be replaced by 2-deoxy-ADP but not by alphabeta-methylene ADP, XDP, IDP, GDP or CDP. Nucleotides that did not protect would not act as substrates. 4. Difference-spectra measurements support the interpretation that addition of NO(3) (-) ions to the enzyme-creatine-MgADP complex causes further conformational changes in the enzyme accompanying the formation of a stable quaternary enzyme-creatine-NO(3) (-)-MgADP complex that simulates an intermediate stage in the transphosphorylation reaction. However, the enzyme structure is partially destabilized by quaternary-complex formation. IDP apparently fails to act as a substrate because it cannot induce the necessary conformational change. This behaviour is compared with that of rabbit skeletal muscle creatine kinase. 5. With pyruvate kinase from rabbit muscle, anions activate in the absence of an activating cation and either inhibit or have no effect in its presence. 6. Both activation and inhibition were competitive with respect to the substrate, phosphoenolpyruvate, and curved double-reciprocal plots were obtained. The results may be interpreted in terms of co-operatively induced conformational changes, and this is supported by difference-spectra measurements. However, the Hill coefficient of 1 was not significantly altered. 7. Inhibition by lactate plus pyruvate is less than additive, indicating that both bind to the same site on the enzyme, whereas that by lactate plus NO(3) (-) is additive, indicating binding at separate sites. It is inferred that a quaternary enzyme-pyruvate-NO(3) (-)-MgADP complex could form, but no evidence was obtained to suggest that it possessed special properties comparable with those found with creatine kinase. The implications of these findings for the unidirectional nature of the mechanism of pyruvate kinase is discussed. 8. Lactate or alpha-hydroxybutyrate could not act instead of pyruvate to form a stable quaternary complex, although both activate the K(+)-free enzyme. Only the former inhibits the K(+)-activated enzyme. The activating cation both lowers the Michaelis constant for phosphoenolpyruvate and tightens up the specificity of its binding site.
TL;DR: Analytical ultracentrifugation showed ribosomes were shown to be in dynamic reversible equilibrium with their subunits, and a thermodynamic analysis was made of the association-dissociation reaction and of several factors which influence it.
Abstract: A systematic study has been made of the dissociation into subunits of the ribosomes of Escherichia coli. By analytical ultracentrifugation, ribosomes were shown to be in dynamic reversible equilibrium with their subunits. This enabled a thermodynamic analysis to be made of the association-dissociation reaction and of several factors which influence it: the concentration of monovalent and divalent cations, the presence of transfer RNA and supernatant factors, the pH, and hydrostatic pressure. The apparent change in free energy for the association in 10 mM sodium phosphate pH 7.0 was–17.4 kcal/mol. Association was accompanied by the net binding of magnesium ions or the net release of monovalent cations (potassium, sodium, or Tris ions). Circular dichroism measurements of ribosomes and their isolated subunits over a range of magnesium and potassium ion concentrations indicated that a change in the conformation of each subunit accompanied association. The change occurring in the 50-S subunit was dependent on the presence of potassium ions, whereas the change in the 30-S subunit was magnesium-ion dependent. The conformational change in the 50-S subunit was critical for the association-dissociation reaction.
Under ionic conditions which lead to ribosome dissociation one molecule of transfer RNA was released per 70-S ribosome. This was an independent reaction which did not influence the subunit association-dissociation equilibrium. The release of transfer RNA was accompanied by the net release of four magnesium ions, and occurred with an apparent change in the free energy of 20.8 kcal/mol.
TL;DR: The potential of the pulse radiolysis method for revealing conformational changes in proteins is demonstrated and a primary binding site exists in the serum albumin molecule, which the results indicate to be a hydrophobic cleft in the surface of the molecule.
TL;DR: It has been concluded that an induced-fit mechanism is not involved in β-amylase action and evidence in support of the involvement of sugar ring distortion during β- amylase catalysis, such as takes place in lysozyme-catalyzed hydrolysis, is presented.
Abstract: 1
The inhibition of β-amylase by cyclodextrins has been studied; cyclomaltohexaose is a considerably more powerful inhibitor than cyclomaltoheptaose.
2
The inhibition of β-amylase by these dextrins is substantially reduced in the presence of dimethylsulfoxide; this has been related to the change in conformation which takes place in the cyclodextrins in dimethylsulfoxide solution.
3
Circular dichroism measurements indicate the lack of a conformational change in β-amylase on interaction with cyclomaltohexaose.
4
It has been concluded that an induced-fit mechanism is not involved in β-amylase action.
5
Evidence in support of the involvement of sugar ring distortion during β-amylase catalysis, such as takes place in lysozyme-catalyzed hydrolysis, is presented.
TL;DR: It is concluded from the spectroscopic data that the proteins are flexible molecules and that tyrosine residues and at least one disulphide chromophore are involved in the conformational change.
Abstract: The sweet-tasting proteins, thaumatin I and II, isolated from the fruits of Thaumatococcus daniellii Benth, both lose their sweetness on heating. Circular dichroism and proton magnetic resonance measurements indicate that the proteins undergo reversible conformational changes as the temperature is increased. Then at a certain temperature, which varies with pH, irreversible heat denaturation occurs. At pH 5.0, the native conformation is most stable and the conformational change is reversible up to 75 °C even on prolonged heating.
We concluded from the spectroscopic data that the proteins are flexible molecules and that tyrosine residues and at least one disulphide chromophore are involved in the conformational change. The results justify the assumption that the irreversible heat-induced conformational transition is responsible for the loss of sweetness of the proteins.
TL;DR: The interaction of αs1-casein with calcium ions at pH 7.0 has been studied, and it is shown that there is a stepwise increase in the fluorescence of the tryptophan residues of the protein as increasing amounts of Ca2+ are added, leading to eventual precipitation of the calcium-caseinate complex.
Abstract: The interaction of αs1-casein with calcium ions at pH 7.0 has been studied, and it is shown that there is a stepwise increase in the fluorescence of the tryptophan residues of the protein as increasing amounts of Ca2+ are added, leading to eventual precipitation of the calcium-caseinate complex.
The first of these steps appears to result from a conformational change induced by Ca2+, without which the protein cannot precipitate. Further steps arise from interaction between protein molecules to produce particles of about 120 nm in diameter, then final aggregation of these particles to give a precipitate. All of these changes result in changes in the fluorescence emission spectra of one or both tryptophan residues in the casein, although most of the change in fluorescence behaviour in the first step of the interaction probably arises from tryptophan-164 in the protein:
TL;DR: The substrate induced conformational change of glutamine binding protein isolated from E. coli has been studied by high resolution proton magnetic resonance spectroscopy and the kinetics of binding as well as a possible mode of action of the binding proteins will be discussed.
TL;DR: The results show that, the metal ions affect, the hydrolysis at the substrate site through a conformational change of the protein, in agreement with significant alterations in the circular dichroism spectrum.
Abstract: A study of the role of divalent metal ions, in particular of Mg2+ and Mn2+ in the reaction of the inorganic pyrophosphatase of bakers' yeast has been carried out. It is shown that the free metal ions compete with each other for the same metal binding site. Binding to this site causes reversible conformational changes of the enzyme as indicated by the kinetics. This assumption is in agreement with significant alterations in the circular dichroism spectrum. In the presence of inorganic pyrophosphate the changes of the enzyme are slow enough to be followed kinetically over a period of minutes. Other possibilities for a slow transition of the enzyme velocity which might exist according to the hysteretic enzyme concept of Frieden could be rejected. To explain the experimental data a kinetic scheme is proposed.
The results show that, the metal ions affect, the hydrolysis at the substrate site through a conformational change of the protein.
TL;DR: The effect of ADP binding to the same enzyme site on the rate of enzymatic ATP hydrolysis is small, although slight activation and inhibition may occur at low and high ATP concentrations, respectively.
TL;DR: The presence of covalently bound DON in some of the protomeric subunits of the tetramer stabilize the remaining protomers in the active (protonated) state at pH values above the normal transition point, and substrate saturation curves are shifted to hyperbolic form and reaction of [14C]DON with the enzyme is promoted at pH 6, at which pH such reaction does not occur in the native enzyme.
TL;DR: The conditions for the formation of a low molecular weight Fragments D (Fragment d) have been elucidated and an irreversible conformational change on incubation at pH values below 3.5 leaves Fragment D more susceptible to additional plasmic digestion.
TL;DR: Additional evidence for ligand-induced, conformational changes is presented; it is shown that ligand protects con A against hydrolysis by pronase and against heat aggregation.
TL;DR: In this paper, the circular dichroism and absorption spectra of particulate and solubilized brain microsomes were reported, and the corrected molar ellipticity for the membrane suspension was −1.1 × 10+4, between the values of axonal and oxyntic cell membranes and those for sarcotubular vesicles.
Abstract: The circular dichroism and absorption spectra of particulate and solubilized brain microsomes are reported. The corrected molar ellipticity for the membrane suspension was −1.1 × 10+4, between the values of axonal and oxyntic cell membranes and those for sarcotubular vesicles. No conformational change was detected which correlated unambiguously with the active cation transport function of these microsomes. Divalent cations, however, elicited a significant change in the membranes' ultra structure. Correction of suspension data for the NaI microsomes with and without sonication gave virtually identical values providing optimism for the corrections used and validating the difference in corrected values for ths suspension with and without magnesium. This indicates that, in addition to causing a change in the state of aggregation, 2 mM magnesium ion may reasonably be considered to effect a change in protein conformation.
TL;DR: The finding that there is a correlation between the stereospecificity of the dehydrogenases and the spectral shift of NADH on binding to these enzymes emphasises the need for more data on this variation of extinction coefficient.