Studies on Polydisperse Systems Using an Air-Driven Ultracentrifuge: Application to Phosphatidylcholine Vesicles

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Abstract
A high-speed air-driven ultracentrifuge (Airfuge) was used to determine the MW and effective specific volume of phosphatidylcholine vesicles. Determination of effective specific volume involved varying the solution density until zero sedimentation of the vesicles occurred. The value obtained for the effective specific volume of 0.9885 ml/g agrees well with previously reported values. The determination of the MW of the vesicles is based on a method in which the fraction of vesicles remaining in an upper fraction of the solution column is compared with the values obtained using standard proteins. The values obtained for the MW of the vesicles range from 1.7 .times. 106-2.3 .times. 106 and are in good agreement with results obtained using the analytical ultracentrifuge and with those previously reported. Possible effects due to the polydispersity of the solute are assessed using theoretical calculations and the possibility of using the Airfuge for the study of other polydisperse systems is discussed.

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