The Experts below are selected from a list of 18 Experts worldwide ranked by ideXlab platform

Donald J Winzor - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of cross linking and scission yields in irradiated polymers from the dose dependence of the weight and z average molecular weights
    Macromolecules, 1990
    Co-Authors: James H Odonnell, Catherine L Winzor, Donald J Winzor
    Abstract:

    A procedure has been developed for the determination of scission and cross-linking fields, G(S) and G(X), in irradiated polymers by combination of the ordinate intercepts of plots of ([Mw(0)/ MW(D)] - 1)/D and ([Mz(0)/A/2(D)] - 1)/D versus dose (D). The required weight- and z-average molecular weight data for a given sample can be obtained by using the Rayleigh and schlieren optical systems, respectively, to record the solute distribution in a single Sedimentation Equilibrium Experiment. The procedure has been tested by application to simulated data for a range of initial molecular weight distributions and values of G(S)/G(X) and applied to previous Sedimentation Equilibrium results (Nichol, J. M.; Donnell, J. H.; Rahman, NLP.; Winzor, D. J. J. Polym. Sci., Polym. Chem. Ed. 1977,15, 2919) for a polystyrene sample with Afw(0)/Mn(0) = 1.03 and G(S)/G(X) = 1.

James H Odonnell - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of cross linking and scission yields in irradiated polymers from the dose dependence of the weight and z average molecular weights
    Macromolecules, 1990
    Co-Authors: James H Odonnell, Catherine L Winzor, Donald J Winzor
    Abstract:

    A procedure has been developed for the determination of scission and cross-linking fields, G(S) and G(X), in irradiated polymers by combination of the ordinate intercepts of plots of ([Mw(0)/ MW(D)] - 1)/D and ([Mz(0)/A/2(D)] - 1)/D versus dose (D). The required weight- and z-average molecular weight data for a given sample can be obtained by using the Rayleigh and schlieren optical systems, respectively, to record the solute distribution in a single Sedimentation Equilibrium Experiment. The procedure has been tested by application to simulated data for a range of initial molecular weight distributions and values of G(S)/G(X) and applied to previous Sedimentation Equilibrium results (Nichol, J. M.; Donnell, J. H.; Rahman, NLP.; Winzor, D. J. J. Polym. Sci., Polym. Chem. Ed. 1977,15, 2919) for a polystyrene sample with Afw(0)/Mn(0) = 1.03 and G(S)/G(X) = 1.

David L. Ollis - One of the best experts on this subject based on the ideXlab platform.

  • Escherichia coli P,, protein: crystallization and oligomeric structure
    1994
    Co-Authors: Subhash G. Vasudevana, Craig Gedye, Nicholas E. Dixon, Eong Cheah, Peter M. Suffolk, Paul D. Carra, Peter D. Jeffreyb, David L. Ollis
    Abstract:

    The Escherichia coli signal transduction protein P,,, product of the glnB gene, was overproduced and purified. The predicted molecular weight of the protein based on the correct nucleotide sequence is 12,427 and is very close to the value 12.435 obtained by matrix-assisted laser desorption mass spectrometry. Hexagonal crystals of the unuridylylated form of P,, with dimensions 0.2 x 0.2 x 0.3 mm were grown and analysed by X-ray diffraction. The crystals belong to space group P6, with a = b = 6 1.6 A, c = 56.3 A and V,,, of 2.5 for one subunit in the asymmetric unit. A low-resolution electron density map showed electron density concentrated around a three-fold axis, suggesting the molecule to be a trimer. A Sedimentation Equilibrium Experiment of the meniscus depletion type was used to estimate a molecular weight of 35,000 f 1,000 for P,, in solution. This result is consistent with the native protein being a homotrimer.

  • Escherichia coli PII protein: purification, crystallization and oligomeric structure.
    FEBS Letters, 1994
    Co-Authors: Subhash G. Vasudevan, P D Jeffrey, Craig Gedye, Nicholas E. Dixon, Eong Cheah, Paul D. Carr, Peter M. Suffolk, David L. Ollis
    Abstract:

    Abstract The Escherichia coli signal transduction protein PII, product of the glnB gene, was overproduced and purified. The predicted molecular weight of the protein based on the correct nucleotide sequence is 12,427 and is very close to the value 12,435 obtained by matrix-assisted laser desorption mass spectrometry. Hexagonal crystals of the unuridylylated form of PII with dimensions 0.2 × 0.2 × 0.3 mm were grown and analysed by X-ray diffraction. The crystals belong to space group P63 with a=b=61.6A,c= 56.3 A and Vm of 2.5 for one subunit in the asymmetric unit. A low-resolution electron density map showed electron density concentrated around a three-fold axis, suggesting the molecule to be a trimer. A Sedimentation Equilibrium Experiment of the meniscus depletion type was used to estimate a molecular weight of 35,000 ± 1,000 for PII in solution. This result is consistent with the native protein being a homotrimer.

Catherine L Winzor - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of cross linking and scission yields in irradiated polymers from the dose dependence of the weight and z average molecular weights
    Macromolecules, 1990
    Co-Authors: James H Odonnell, Catherine L Winzor, Donald J Winzor
    Abstract:

    A procedure has been developed for the determination of scission and cross-linking fields, G(S) and G(X), in irradiated polymers by combination of the ordinate intercepts of plots of ([Mw(0)/ MW(D)] - 1)/D and ([Mz(0)/A/2(D)] - 1)/D versus dose (D). The required weight- and z-average molecular weight data for a given sample can be obtained by using the Rayleigh and schlieren optical systems, respectively, to record the solute distribution in a single Sedimentation Equilibrium Experiment. The procedure has been tested by application to simulated data for a range of initial molecular weight distributions and values of G(S)/G(X) and applied to previous Sedimentation Equilibrium results (Nichol, J. M.; Donnell, J. H.; Rahman, NLP.; Winzor, D. J. J. Polym. Sci., Polym. Chem. Ed. 1977,15, 2919) for a polystyrene sample with Afw(0)/Mn(0) = 1.03 and G(S)/G(X) = 1.

Peter Schuck - One of the best experts on this subject based on the ideXlab platform.

  • Sedimentation Analysis of Noninteracting and Self-Associating Solutes Using Numerical Solutions to the Lamm Equation
    Biophysical Journal, 1998
    Co-Authors: Peter Schuck
    Abstract:

    The potential of using the Lamm equation in the analysis of hydrodynamic shape and gross conformation of proteins and reversibly formed protein complexes from analytical ultracentrifugation data was investigated. An efficient numerical solution of the Lamm equation for noninteracting and rapidly self-associating proteins by using combined finite-element and moving grid techniques is described. It has been implemented for noninteracting solutes and monomer-dimer and monomer-trimer equilibria. To predict its utility, the error surface of a nonlinear regression of simulated Sedimentation profiles was explored. Error contour maps were calculated for conventional independent and global analyses of Experiments with noninteracting solutes and with monomer-dimer systems at different solution column heights, loading concentrations, and centrifugal fields. It was found that the rotor speed is the major determinant for the shape of the error surface, and that global analysis of different Experiments can allow substantially improved characterization of the solutes. We suggest that the global analysis of the approach to Equilibrium in a short-column Sedimentation Equilibrium Experiment followed by a high-speed short-column Sedimentation velocity Experiment can result in Sedimentation and diffusion coefficients of very high statistical accuracy. In addition, in the case of a protein in rapid monomer-dimer Equilibrium, this configuration was found to reveal the most precise estimate of the association constant.

  • Rapid determination of molar mass in modified Archibald Experiments using direct fitting of the Lamm equation.
    Analytical Biochemistry, 1998
    Co-Authors: Peter Schuck, David B. Millar
    Abstract:

    Abstract A new method is described that allows measurement of the molar mass of the solute within 15 to 30 min after start of a conventional long-column Sedimentation Equilibrium Experiment. A series of scans of the concentration distribution in close vicinity of the meniscus, taken in rapid succession after the start of the centrifuge run, is analyzed by direct fitting using the Lamm equation and the Svedberg equation. In case of a single solute, this analysis of the initial depletion at the meniscus reveals its buoyant molar mass and Sedimentation coefficient with an accuracy of approximately 10% and provides gross information about sample heterogeneity. This method can be used to study macromolecules that do not possess the prolonged stability needed in conventional Sedimentation Equilibrium Experiments and it can increase the efficiency of Sedimentation Equilibrium Experiments of previously uncharacterized samples.