Cooperative Binding to Linear Biopolymers

Schwarz, Gerhard; Klose, Sigmar; Balthasar, Wolff

doi:10.1111/j.1432-1033.1970.tb00872.x

Cited by 160 publications

(82 citation statements)

References 11 publications

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“…Cooperative Binding Processes. Cooperative stacking of dyes on polyanions is a common phenomenon [20,21]. Intercalating ligands show this phenomenon in binding to DNA only at much higher free dye concentrations than those present in our determination of a values.…”

Section: Spec(fi'cifj~mentioning

confidence: 69%

Interactions of Heteroaromatic Compounds with Nucleic Acids

Müller

Crothers

1975

European Journal of Biochemistry

359

188

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We have examined the origins of base specificity in intercalating ligands by studying the interaction with DNA of a series of proflavine and acridine orange analogs differing in the heteroatoms present in the chromophore. Base specificity was determined by differential dialysis of the dye against DNA samples of differing G . C content. We find that G . C specificity increases as the visible absorbance band of the chromophore moves to longer wavelength, implying a relation between specificity and polarizability of the chromophore. This can be rationalized by recognizing that the G . C pair is more polar than A . T, and should therefore interact more favorably with an easily polarized ring system.We find in addition that dimethylation of the chromophore amino groups increases specificity which we discuss in terms of steric and coupled steric-electronic contributions.Our results also bear on the origin of G . C specificity in binding actinomycin to DNA. Some of the compounds studied are as G . C specific as actinomycin, yet they lack hydrogen-bonding functions as plausible determinants of specificity. This observation gives new life to the hypothesis that the specificity of actinomycin is determined primarily by preferential interaction of the chromophore with a G . C pair.It has long been known that many small, positively charged molecules interact with nucleic acids; these compounds have been widely used for analytical, diagnostic and therapeutic purposes. Of special importance in this regard are planar, heterocyclic molecules, including many natural and synthetic dyestuffs [I]. In this series of papers we address ourselves to an important but relatively neglected aspect of their interaction with DNA, namely the nature and origin In this paper we report a systematic examination of the influence of heteroatoms X and Y on the base and sequence specificity of DNA ligands of the type I. The starting point for this series of experiments was the observation of Muller and Crothers [4] that Eur.

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Section: Spec(fi'cifj~mentioning

confidence: 69%

Interactions of Heteroaromatic Compounds with Nucleic Acids

Müller

Crothers

1975

European Journal of Biochemistry

359

188

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“…There is evidence that initial events in coupling of weak oscillating electromagnetic fields to cell membranes occur on membrane surface polyanionic glycoproteins, producing transient coherent states of nearest-neighbor fixed-charge sites (27). These coherent states may exist for considerable distances along the membrane surface (28), and thus would appear likely sites for the first steps in transductive coupling. Binding and release of Ca2" at these membrane surface sites correlate closely with exposure to certain weak electromagnetic fields.…”

Section: Discussionmentioning

confidence: 99%

Effects of electromagnetic stimuli on bone and bone cells in vitro: Inhibition of responses to parathyroid hormone by low-energy low-frequency fields

Luben

Cain

Chen

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

268

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Low-energy electromagnetic fields pulsed at frequencies of 10-90 Hz significantly increase healing ofchronic fracture nonunions in man. These fields are effective at tissue current levels several orders of magnitude lower than those required for transmembrane depolarization ofnormal cells. We have examined the effects of two clinically used pulsed electromagnetic fields on cultures of the osteoblast-like mouse bone cell line MMB-1. Both fields significantly reduced cellular production of cAMP in response to parathyroid hormone and osteoclast activating factor. Neither basal nor fluoride-activated levels of adenylate cyclase were altered in membranes from cells cultured in the fields; however, the same membrane -preparations exhibited markedly inhibited responses to parathyroid hormone. The fields blocked the inhibitory effects of the hormone on collagen synthesis by MMB-1 cells. However, there was no effect on the inhibition of collagen synthesis by 1,25-dihydroxyvitamin D3, which is believed to act primarily by a nuclear, rather than by a membrane-dependent, mechanism. No significant differences were noted between effects of the two fields, one generating continuous pulse trains (72 Hz) and the other generating recurrent bursts (15 Hz) of shorter pulses. We hypothesize that these field effects are mediated primarily at the plasma membrane of osteoblasts, either by interference with hormone-receptor interactions or by blocking of receptor-cyclase coupling in the membrane. These responses occurred with induced extracellular fields of 1 mV/cm or less, even though transmembrane potential gradients are typically 105 V/cm.Clinical studies (1-5) have demonstrated the usefulness ofelectromagnetic fields in stimulatinghealing ofchronically ununited fractures in humans. Devices generating such fields have been approved for clinical use. However, the mechanisms of action of these fields are not clear. Oscillating electromagnetic fields proven effective in clinical use generate electrochemical gradients in the tissue fluid surrounding cells (6), but these gradients are considerably weaker than the levels required to depolarize cell membranes. Typically, the devices in question impose -20-G pulsed magnetic fields, which induce current densities of -1 uA/cm2 and associated electric gradients of 1-10 mV/cm in extracellular fluids (2). Because of the high resistance ofcell membranes, any transmembrane electrical components ofimposed fields would be lower than the extracellular gradients by two to three orders of magnitude (6) and thus as much as six orders of magnitude less than the typical excitatory threshold currents of 1 mA/cm2 observed for axonal depolarization (7).It would therefore appear that the effectiveness ofsuch weak stimuli in generating cellular processes must depend on a series of amplification mechanisms, either before or during the transmembrane coupling of the initial stimulus (8). Likely loci for amplification and extension of weak electrochemical triggering events at the cell membrane may involve ...

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“…The theoretical curve drawn taking g = 0.6 and a "stacking-coefficient" q = 1470 seems to fit the experimental data well. The high value of the stacking coefficient, higher than that associated with the system of acridine orange, and sodium polyphosphate [22] and close to that found for the system of acridine orange and poly(L-glutamic acid) [32], indicates that the fraction of phosphornonoester groups of phosvitin which are available for the binding of acridine orange (see above) are indeed capable of assuming an optimum geometry most favourable for interaction with pairs of stacked acridine orange molecules.…”

Section: Infrared and Circular-dichroisrn Spextramentioning

confidence: 73%

Polyelectrolyte Behaviour of Phosvitin

Giancotti

Quadrifoglio

Crescenzi

1973

European Journal of Biochemistry

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The results of spectroscopic and microcalorimetric measurements on dilute aqueous solutions of phosvitin are described. Our infrared and circular dichroism spectra show that the phosphoprotein chains may assume either random-coiled or partially helical or /?-structures depending upon the pH. The transition to the low p H 8-form occurs with a distinct cooperative character.The strongly interdependent ionization of fixed charges densely spaced along phosvitin chains, typical of highly charged polyelectrolytes, is well illustrated by the calorimetric enthalpy of protonation data.The interaction of phosvitin with acridine orange in dilute aqueous solution (pH -5) has been studied by means of spectral and equilibrium dialysis experiments. For relatively low polymer to dye concentration ratios, bound acridine orange exhibits a y-type spectrum thus suggesting aggregation of dye molecules onto the protein. Gradual decrease in the extent of bound acridine orange aggregation is produced by increasing the concentration of the protein ; the monomerically bound form is hardly obtained, however, even at relatively high phosvitin concentrations. Binding curves reveal a cooperativity character for the dye-protein interaction.It is suggested that about 60°/, only of phosphomonoester side groups of phosvitin are available for acridine orange binding, these being characterized by a high "stacking" coefficient.The results are tentatively discussed on the basis of present information on phosvitin chemical composition and conformation.The phosphoprotein phosvitin is an atypical biopolymer in that, owing mainly to the high negative charge density along the chain, it is present in aqueous solution at around pH 7 in an essentially unordered conformation [l -31. Gradual protonation of the secondary acidic functions of the phosphomonoester side-groups of phosvitin (0-phosphoserine accounts for more than half of the amino acid residues, while carboxyl groups account for another 12O/, of the total residues [4]) would permit, by reducing interchain electrostatic interactions, the formation of some ordered regions along the polypeptide backbone [2,3]. Finally, by lowering the pH of a dilute aqueous solution of phosvitin down to about 1.8, where also the dissociation of the primary acidic function of the phosphomonoester groups is suppressed, the protein undergoes a conformational transition to a &form We wish to report here the results of a research carried out i n our laboratory on different aspects of the behaviour of phosvitin in dilute aqueous solution. The first section of the paper includes the resultv of a series of microcalorimetric measurements of the enthalpy of protonation of phosvitin in a wide pH range, and infrared and circular dichroism (CD) studies in the entire accessible range of the degree of protonation of the protein. These results provide new information on the polyelectrolyte behaviour of phosvitin and on the ability of its chain to assume Werent conformations depending upon the pH of the solutions. Evidence is presente...

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Cooperative Binding to Linear Biopolymers

Cited by 160 publications

References 11 publications

Interactions of Heteroaromatic Compounds with Nucleic Acids

Interactions of Heteroaromatic Compounds with Nucleic Acids

Effects of electromagnetic stimuli on bone and bone cells in vitro: Inhibition of responses to parathyroid hormone by low-energy low-frequency fields

Polyelectrolyte Behaviour of Phosvitin

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