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Showing papers on "Conformational change published in 1968"


Journal ArticleDOI
TL;DR: The physical property which distinguishes actinomycin from the simpler analogs (which lack biological activity) is a very slow dissociation reaction, several orders of magnitude slower than for the non-active analogs.

794 citations


Journal ArticleDOI
20 Jul 1968-Nature
TL;DR: This work has shown that the modifying effect on enzyme activity probably results from an induced conformational change in the enzyme structure.
Abstract: THE regulation of enzyme activity by cellular metabolites in micro-organisms is usually exerted by feedback control, an initial enzyme of a pathway being controlled by an end-product of that pathway. Such control of enzyme activity has, in many cases, been shown to be “allosteric”—that is, the end-product effector binds to the enzyme at a site distinct from the catalytic (active) site. The modifying effect on enzyme activity probably results from an induced conformational change in the enzyme structure.

108 citations


Journal ArticleDOI
TL;DR: In a previous communication by Penniston et al.l, the multiple configurational states of the inner membrane of the mitochondrion were shown to be determined both by the conformation of the repeating units and by the mode of the cristae.
Abstract: In a previous communication by Penniston et al.l in these PROCEEDINGS, the multiple configurational states of the inner membrane of the mitochondrion were shown to be determined both by the conformation of the repeating units (nonenergized, energized, or energized-twisted) and also by the mode of the cristae (orthodox, aggregated, or comminuted). The conformational changes in the repeating units were constant and independent of the mode of the cristae, but the electron microscopic expression of these conformational changes at the membrane level was profoundly affected by the mode of the cristae. Table 1 summarizes

73 citations


Journal ArticleDOI
TL;DR: Evidence is presented for the existence of several ligand-stabilized forms of aspartate transcarbamylase, as identified by their susceptibilities to proteolysis, and it appears that the primary target of tryptic attack is the regulatory subunit.

67 citations


Journal ArticleDOI
TL;DR: Optical rotatory dispersion and circular dichroism have been used to investigate the protonation of guanosine and some of its analogues and an inversion of the principal Cotton effect and the dichroic band is observed below the acid pK.

59 citations


Journal ArticleDOI
TL;DR: A model for hemoglobin is proposed and its application to allosteric enzymes is discussed with particular reference to asparate transcarbamylase, with results comparing favorably with experiment and a number of specific predictions are made.
Abstract: A model for hemoglobin is proposed and its application to allosteric enzymes is discussed with particular reference to asparate transcarbamylase. The main assumptions made are that the molecule is composed of subunits and that occupation of a sub-unit produces a conformational change which affects the occupational probability of neighboring subunits. The results compare favorably with experiment and a number of specific predictions are made for aspartate transcarbamylase.

52 citations


Journal ArticleDOI
TL;DR: Thermodynamic data indicate that the interaction of AAG with the Δ4-3-ketosteroids is associated with a negative free energy change, composed of a negative enthalpy change and a positive entropy change.

51 citations



Journal ArticleDOI
TL;DR: The data presented support the view that the presence of the competitive inhibitor in the active center region alters the proteolytic susceptibility of bonds at multiple sites, situated outside of this region.

36 citations


Journal ArticleDOI
TL;DR: These experiments show the close interaction of the two chains in the α β dimer and are further evidence that the αβ dimer is the fundamental unit of both structure and function.

35 citations


Journal ArticleDOI
TL;DR: It is suggested that the conformational change responsible for allosteric behavior is a slight quaternary rearrangement, rather than a tertiary structural change which modifies the active centers of aspartate transcarbamylase.

Journal ArticleDOI
TL;DR: Support for the hypothesis that potassium stimulation of pig heart propionyl-CoA carboxylase caused a conformational change on the enzyme was obtained by demonstrating that both the rate of binding of N-[14C]ethyl maleimide and loss of enzymic activity caused by N-ethylmaleimide increased in the presence of K+.

Journal ArticleDOI
TL;DR: A sequential model to explain cooperative effects in proteins such as hemoglobin and feedback enzymes is developed in which it is assumed that a ligand can induce a conformational change in an individual subunit and that the distortion in this one subunit may be transmitted with varying efficiencies to neighboring subunits.


Journal ArticleDOI
TL;DR: The conformational change of β-lactoglobulin A induced by sucrose is made apparent, in the absence of any enzymatic reaction, by titration and difference spectroscopy curves, which are all the more plausible since interactions in a macromolecule often go with changes in the tertiary and quaternary structure.

Journal ArticleDOI
TL;DR: In this paper, the authors studied how the medium affects the hydrodynamic and optical behaviour of polymethacrylic acid (PMAA) molecules in solution, as well as the influence of the birefringence and viscosity of solutions of a number of PMAA fractions in acidified water (0.002 ~ HC1), methanol and mixtures of both.
Abstract: THE intrinsic viscosity [7] of nonionized polymethacrylic acid (PMAA) changes by a factor of three or four on transition from aqueous to alcoholic solutions, although both water and methyl alcohol are 9-solvents for this polymer [1-6]. The big change in Lu] is generally at t r ibuted to conformational changes in the macromolecule due to the breakdown of the secondary structure which is possessed in an aqueous medium. At the same time there is very good evidence in support of the suggestion that hydrophobic interactions in the macromolecule preserve its secondary structure [6-8]. However the behaviour of PMAA molecules in methanol is quite different from that of flexible macromolecules in solution. Much therefore remains to be elucidated in connection with the problem of the conformational change in the PMAA molecule. In this investigation we studied how the medium affects the hydrodynamic and optical behaviour of PMMA molecules in solution, as well as the influence of the birefringence and viscosity of solutions of a number of PMAA fractions in acidified water (0.002 ~ HC1), methanol and mixtures of both. The method polymerization of PMAA was also considered in regard to its effect on the hydrodynamic properties of the macromolecules.

Journal ArticleDOI
TL;DR: The preferred rotational conformation of the acetyl group of (−)-10-nor-8-oxoneomenthol (I), (−)- 10-nor 8 -oxone-menthols (I, II), (−-10-or-8 -oxon-mentshol (II, III, and IV) has been examined by a combination of conformational analysis by a priori calculation and variable-temperature circular dichroism and infrared spectrum measurements as mentioned in this paper.
Abstract: The preferred rotational conformation of the acetyl group of (+)-10-nor-8-oxoneomenthol (I), (−)-10-nor-8-oxomenthol (II), (−)-10-nor-8-oxocarvomenthol (III), and (+)-10-nor-8-oxoneocarvomenthol (IV) has been examined by a combination of conformational analysis by a priori calculation and variable-temperature circular dichroism and infrared spectrum measurements. Compound I exhibited an inversion in the sign of the Cotton effect upon a change in the solvent. This phenomenon was interpreted as indicating the conformational change Ia\ightleftarrowsIb. The cause of the change was ascribed to the formation and subsequent rupture of the intramolecular hydrogen bond. Compound II exhibited a solvent-depending circular dichroism curve similar to the curve of I; this was explained as indicating the existence of a conformational equilibrium between the free conformer, IIa, and the internally-hydrogen-bonded conformers, IIb, IIc, and IId. Furthermore, compounds III and IV were found to take preferentially the IIIa–I...