We develop series expansions useful in extrapolating two-angle light-scattering data to 0 degrees using the Debye expression for the form factor of a Gaussian coil. Errors that would be encountered if the equations were used to analyze data on molecules of other shapes are discussed. Graphs show the percent error in radius of gyration (R(g)) and molecular weight (M(w)) for hard spheres, rigid rods, and flexible rings over the range of R(g) = 0-150 nm. Finally, we present experimental data showing that instrument calibration done in one solvent can be used in other solvents with different index of refraction and that accurate values of dn/dc can be obtained using a commercially available refractive index detector.

The diffusion constant of phenylalanyl-tRNA synthetase has been measured by laser light scattering under conditions of complex formation with Mg2+, L-phenylalanine, MgATP, tRNAPhe, modified tRNAPhe, tRNAPhe (yeast), and noncognate tRNA. The diffusion constant (pH 7.5, 20 degrees C) of the free enzyme is (2.85 +/- 0.005) x 10(-7) cm2 s-1, of the enzyme . Mg2+ complex (2.40 +/- 0.05) x 10(-7) cm2 s-1 and of the enzyme . Mg2+ . tRNAPhe complex (2.95 +/- 0.06) x 10(-7) cm2 s-1. The effect of tRNAPhe is only seen when the enzyme is saturated with Mg2+. The smaller substrates exhibit no effect besides a small increase of the value of the diffusion constant under conditions where the enzyme-phenylalanyladenylate is synthesized. Of the noncognate tRNATyr and tRNAIle, the latter is able to associate with the enzyme, causing the value of the diffusion constant to increase. tRNAPhe (yeast) and tRNAhvPhe (photo-cross-linked tRNAPhe) exhibit similar effects. The observed variation of the diffusion constant is attributed to conformational changes of the enzyme. The opposite effects of Mg2+ and tRNAPhe are interpreted as an expansion and recontraction, respectively, of the enzyme molecule. In several cases, the effects were used to follow a titration of the enzyme with a ligand. Dissociation constants were calculated from the resulting titration curves, yielding values which are in agreement with those obtained by other techniques. It is established by comparison that of the two possible binding sites for each Mg2+ and tRNAPhe the diffusion constant reflects occupation of only a single class of sites.

The rotational relaxation time of poly(p-phenylene benzbisthiazole) (PBT) has been used to characterize its conformation in chlorosulfonic acid solutions. We present a method of extracting the persistence length from the forward depolarized photon correlation data. Using Hearst’s theory for the rotational diffusion coefficient of a wormlike chain, a persistence length of 640 Å is determined. The results also suggest that under certain conditions depolarized photon correlation spectroscopy is a potentially useful method for estimating the polydispersity of a polymer sample.

Photon-correlation spectroscopy is a powerful technique for measuring the translational diffusion coefficient of particles and macromolecules in solution. In the study described here, this technique was used to analyze a specific dimerization process involving the association of two tRNA molecules through complementary anticodons. The tRNAs used in the analysis were E. coli tRNA and yeast tRNA Phe . The experimental data on the concentration dependence of the observed diffusion constants are shown to agree well with theoretical predictions. From these data, the equilibrium constant of the association reaction was determined for dimers formed over a wide range of temperatures and in several different solution conditions. In solutions of 0.1 M ionic strength at 22°C, the equilibrium constants vary from 1 × 10 5 M −1 in the absence of magnesium to 1.5 × 10 6 M −1 in 10 m M Mg +2 . The enthalpy and entropy changes for dimer formation in the absence and presence, 5 and 10 m M , of magnesium have been obtained from the temperature dependence of the equilibrium constant. The results show that both Δ H and Δ S contribute to the free energy of binding and that their relative contributions are similar for each solution condition evaluated.

0021-9797/78/0632-0290502.00/0 Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved. become important and, in extreme cases, the solute molecules may assume a high degree of order (6); and (2) it is necessary to understand the effects of charge on measurements made on dilute solutions in order to analyze the data in terms of the hydrodynamic properties of the solute molecules. A complete theory of the effects of charge on light scattering measurements is not yet available. However, in the dilute solution limit we may use the theory of Stephen (7). The result of interest to us here is that when the Debye shielding length is small compared with the scattering wavelength, the measured diffusion constant may be expressed as

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuasielastic Light Scattering: An Experimental Study of PolydispersityM. Schmidt, W. Burchard, and N. C. FordCite this: Macromolecules 1978, 11, 3, 452–454Publication Date (Print):May 1, 1978Publication History Published online1 May 2002Published inissue 1 May 1978https://pubs.acs.org/doi/10.1021/ma60063a003https://doi.org/10.1021/ma60063a003research-articleACS PublicationsRequest reuse permissionsArticle Views168Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Laser light scattering has been used to evaluate conformational differences between free 16S RNA and several specific protein-16S RNA complexes. Proteins that interact strongly with the 16S RNA early in subunit assembly stabilize the RNA chain against unfolding in 1 mM Mg2+ and actually promote the formation of a more compact teriary structure in 20 mM Mg2+. A vital function of these proteins may therfore consist in altering the configuration of the RNA so that further assembly reactions can take place.

A small-angle intensity fluctuation spectrometer has been constructed and used to measure the width G of the Rayleigh component of 514.5-nm light scattered from liquid helium. The techniques utilized to maximize the weak scattered signal are described. Measurements of G at small angles (65TP<1.42 MPa) agree with predictions based on hydrodynamic theory.

Laser light scattering is shown to be an effective means of obtaining a rapid, objective assessment of dynamic changes in the intact plasmodium of the myxomycete Physarum polycephalum during bidirectional (shuttle) streaming. The motion of material in a 100 mum diameter region of a plasmodial vein was studied by following changes in the autocorrelation function of the fluctuations in the scattered light intensity. The autocorrelation function was recorded at 10 s intervals and analyzed to follow changes in the flow velocity of protoplasm associated with shuttle streaming. Rhythmic velocity changes and a "beating" pattern of velocity maxima were readily observed. In an attempt to locate the site of underlying structural changes in the vein responsible for the changing pattern of flow, the average scattered intensity was separated into components derived from moving and stationary scatterers. Periodic variations in the light intensity due to stationary scatterers are related to the streaming cycle and indicate the occurrence of important structural changes in the vein walls. Two possible interpretations of the data are offered; one involving gross dynamic changes in vein structure, the other involving the formation, contraction, or breakdown of fibrillar material in the vein wall during the streaming cycle.

The diffusion constants of Escherichia coli transfer ribonucleic acid and phenylalanine-specific tRNA from yeast have been determined under a variety of solution conditions using the technique of laser light scattering. The results reveal that a major change occurs in the conformation of tRNA when the ionic strength is reduced from 0·2 m to 0·1 m in the presence of 1·0 mm-magnesium at pH 7·2 and 20°C. The diffusion constant of the low salt conformer is greater by 11%, indicating that it is significantly more compact than the high salt form. A ‘block and hinge’ model is proposed to explain the conformational change. The results also reveal that a readily reversible association of bulk tRNA occurs in 10 mm-magnesium at high ionic strength at 20°C with an association constant of about 103 m−1. The association constant is similar to that reported by others for the formation of dimers between tRNAs with complementary anticodons under similar conditions. The surface charge of unfractionated E. coli tRNA has been estimated from the diffusive virial coefficients. In 1 mm-MgCl2 the average charge per tRNA is ten electrons, while at 10 mm-MgCl2 there are eight electrons per molecule.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has an important role in glycolysis, and in recent years it has been studied as a possible glycolytic control point.Both the yeast and rabbit muscle enzyme undergo temperature-dependent dissociation in the presence of ATP (1-3).This study further defines the physical behavior of this enzyme through measurements of its translational diffusion coefficient, D,, and gives evidence for some conformational changes in the enzyme.By measuring the half-width of the spectrum of the light scattered from a solution of enzyme, it is possible to determine D, of the molecule (4-6).D, can then be related, through hydrodynamic parameters, to molecular size and shape.By concurrently measuring the intensity of scattered light, molecular weight changes may also be fol- lowed.Thus in one experiment it is possible to obtain independent parameters related to conformation and molecular weight changes.Our results show that this enzyme has a distinct tendency to form aggregates (to which the scattered intensity is very sensi- tive), that it shows a temperature-dependent dissociation, and that, in the presence of ATP, there is a conformational change with temperature, distinct from the aforemen- tioned changes in quarternary structure.Rabbit muscle enzyme was obtained from the Sigma Chemical Co., St. Louis, Mo. (lot number 63C-9530).Crystals of the enzyme were collected by centrifugation and dissolved in buffer I (0.1 M imidazole, 1 mM dithiothreitol (DTT), 1 mM ethylene- diaminetetraacetic acid (EDTA), pH 7.15).This solution was then dialyzed overnight against 1 liter of buffer I and run through a 1 x 18-in Sephadex G200 column (Pharma- cia Fine Chemicals, Inc., Piscataway, N. J.).The enzyme was then reconcentrated using an Amicon filtration unit (Amicon Corp., Lexington, Mass.) and UMlO filters.Solutions not purified by column chromatography contained aggregates which com- pletely dominated the scattering spectrum.A different lot of enzyme showed the same behavior.All samples were prepared within one day of the experiment, as it was found that a sample aggregated enough after one day's storage to significantly affect mea- sured values of D,.All purification steps were carried out at 4°C.Concentrations

We have determined the relative liquid and vapor densities $\frac{{\ensuremath{\rho}}_{L}}{{\ensuremath{\rho}}_{c}}$ and $\frac{{\ensuremath{\rho}}_{V}}{{\ensuremath{\rho}}_{c}}$ along the coexistence curve in ${\mathrm{SF}}_{6}$ using capacitance measurements of the dielectric constant together with an independent determination of the dielectric-constant-density relationship. Near the critical point, the diameter ${\ensuremath{\rho}}_{d}=\frac{1}{2}({\ensuremath{\rho}}_{L}+{\ensuremath{\rho}}_{V})$ exhibits a successively larger departure from the extrapolated linear dependence on temperature. This feature is characteristic of many liquid-vapor critical-point models, but it has not been previously observed.

Using an optical beating technique, the diffusion coefficients and relative scattered intensity of Escherichia coli 70S, 50S, and 30S ribosomes are measured as a function of temperature and Mg(2+) concentration. For solutions at 10 mM Mg(2+) and between 0 degrees C and about 40 degrees C, the values of D(20,w) obtained are 1.7, 1.9, and approximately 2.1 x 10(-7) cm(2)/s, respectively. Preparative procedures drastically affect these values and equivalent hydrodynamic ellipsoids of revolution models give large axial ratios indicating extensive hydration or a deviation from the assumed shape. Calculations also indicate that the subunits expand upon dissociation. Measurements of D(20,w) vs. temperature indicate that 70S particles undergo a conformational change prior to dissociation and can be heat dissociated at 30-32 degrees C at low concentrations. Treatment of 70S ribosomes with EDTA causes a biphasic dissociation reaction. Addition of Mg(2+) after dissociation with EDTA shows that longer waiting times yield fewer 70S particles and that even short waiting times may yield ribosomes differing from the native conformation. Addition of p-chloromercuribenzoic acid (PCMB) is shown to dissociate 70S particles, but to a lesser extent than ethylenediaminetetraacetic acid (EDTA).