Polyethylene glycol solubility gradients, a new and rapid technique for investigations of plant viruses

Abstract

A simple method for determining the solubility of plant viruses and other macromolecules in aqueous solutions of polyethylene glycol (PEG) is described. The method involves centrifugation of PEG-precipitated virus through a reverse concentration gradient of PEG, MW 6000, incorporated and stabilized in a positive sucrose gradient. The concentration of PEG at which the virus particles resolubilize is termed the solubility concentration.The solubility concentration of virus particles for a number of model systems was dependent upon their surface/volume ratio and their surface charge characteristics, the latter in turn depending on the pH and ionic conditions existing within the solubility gradient.Solubility gradient centrifugations were of value both analytically, in providing information for purification procedures and in the characterization of viruses and virus strains, and preparatively, allowing separation of certain morphologically or electrophoretically distinct components. The technique of solubility gradient centrifugation is potentially applicable to other systems having distinct solubility characteristics in an appropriate solvent.