The accuracy of the Svedberg oil-turbine ultracentrifuge

Abstract

1. Studies on samples of different tissues collected during three seasons from Juglana regia trees growing in several districts round London showed, in the endocarp, remarkably high concentrations of vitanin C, which may be used in lignification. This vitamin C probably originates mainly in photosynthetic centres in the leaves.2. Examination of the intervening tissues showed that physiological conditions (acidity, concentration of enzymes and of vitamin C) militate against translocation of vitamin C as such from leaf to nut. The experimental findings favour an alternative hypothesis, which will be considered later.

Improving the thermal, radial, and temporal accuracy of the analytical ultracentrifuge through external references

“…For this purpose, we draw on a data set of more than one hundred measurements of s -values of a stable standard protein in eleven instruments collected over the course of 18 months, originally conducted to assess data consistency in our laboratories. The immediate motivation to revisit these calibration problems was generated by the measurement of large differences in s -values of highly pure EGFP conducted on different instruments and with different optical systems [46], reminiscent of putative, initially unrecognized, or established temperature calibration errors in previous studies by others [41,47-51]. The present work further refines the question of time calibration we have previously communicated [40], and additionally addresses calibrations in temperature and radius.…”

“…Based on this, a correction algorithm was implemented in the program SEDFIT to completely eliminate this issue from further entering the data analysis [40]. Among the other required calibrated measurements, the distance from the center of rotation and the rotor temperature have previously been identified as the most critical and potentially limiting [20,41,42], the latter due to the strong temperature dependence of the aqueous solvent viscosity. In the most recent study on the absolute accuracy of s -values that can be determined by SV, Errington & Rowe identified the temperature as a leading instrumental source of systematic errors, and estimated the accuracy of s -values to be at best within ± 2-3% [42].…”

“…These include devices based on calibrated thermocouples [52–54], infrared radiation [51,55], the melting point of solids [41,48,52], and the use of solutions with temperature-sensitive absorbance properties [49]. Radiometers are now used in the commercial instruments, and routine temperature verification by the manufacturer is performed by a post-centrifugal temperature analysis using a calibrated thermometer.…”

Specificity of glucose oxidase (notatin)

“…According to the published determinations of sedimentation velocity and diffusion constant the molecular weight of notatin is 152,000 (Cecil & Ogston, 1948a). Following an investigation into the accuracy of the ultracentrifugal method which involved corrections for errors in cell temperature (Cecil & Ogston, 1948b) Dr R. Cecil has re-examined notatin sample Y (410-417) and has amended S20 x 1013 from 8-27 to 8-09 which corresponds to a molecular weight of 149,000.…”

Improved measurement of the rotor temperature in analytical ultracentrifugation

“…Unfortunately, a measurement of the sample solution temperature in a spinning rotor is non-trivial and many methods have been developed during the long history of AUC. These include devices based on calibrated thermocouples [1,5,6], methods based on the observation of the melting point of solids [7,8], radiometers [9,10], and thermochromic solutions [11]. A radiometer is currently implemented in the ProteomeLab analytical ultracentrifuge (Beckman Coulter, Indianapolis, IN).…”