Amvn viscometer

The viscosity of electrolyte solution with increasing concentrations of glucose was measured with an AMVn viscometer (Anton Paar) apparatus at room temperature (~22 °C).

Sedimentation equilibrium experiments were carried out in a buffer of 20 mM HEPES pH 7.5, 100 mM NaCl and 1 mM TCEP. Samples were loaded into 12 mm six-sector cells, placed in an An-50Ti rotor and centrifugated at 10,200, 12,200 and 21,000 rpm at 20 °C until equilibrium had been reached using an Optima XL-I analytical ultracentrifuge (Beckman). The data were analysed in SEDPHAT 15.2b^{68 (link)}. The partial-specific volumes (v-bar) were calculated using Sednterp^{69 (link)}. The density and viscosity of the buffer were determined with a DMA 4500 M density metre (Anton Parr) and an AMVn viscometer (Anton Paar). Data were plotted with the program GUSSI⁷⁰ .

Experiments were conducted in a ProteomeLab XL-I analytical ultracentrifuge (Beckman Coulter) following standard protocols (31 ). All samples in a buffer containing 20 mM Tris, pH 7.5, 200 mM NaCl, and 5 mM DTT were loaded into a cell assembly composed of a double sector charcoal-filled centerpiece with a 12-mm path length and either quartz or sapphire windows. The density and viscosity of the ultracentrifugation buffer at 20 °C were measured with a DMA 5000 M density meter and an AMVn viscometer (both Anton Paar), respectively. The cell assembly in the sedimentation velocity experiments contained identical sample and reference buffer volumes of 300 μl was placed in a rotor and temperature equilibrated at rest at 20 °C for 2 h before it was accelerated from 0 to 50,000 rpm. Rayleigh interference optical data were collected at 1-min intervals for 12 h. The velocity data were modeled with diffusion-deconvoluted sedimentation coefficient distributions c(s) in SEDFIT (32 ), using algebraic noise decomposition and with signal-average frictional ratio and meniscus position refined with nonlinear regression. The s-value was corrected for time, temperature, and radial position, and finite acceleration of the rotor was accounted for in the evaluation of Lamm equation solutions (33 (link)).