Publisher Summary
This chapter discusses the density gradient centrifugation and its application to plant viruses. The chapter discusses the numerous possible modifications of this method that are classified in three categories. The term “isopycnic gradient centrifugation” is used for methods in which centrifugation is continued until each particle has reached a point where the suspending medium has a density equal to that of the particle. The other two categories of methods are called “rate zonal centrifugation” and “equilibrium zonal centrifugation.” Density gradient centrifugation is a zonal separation procedure that is applicable to many problems requiring separations of particles according to size or density. It provides an efficient separation of comparatively small quantities of virus. There is no lower limit to the concentration of virus that may be used because the superimposed density gradient prevents convection. The requirement for small quantities is a disadvantage if it is desired to purify a quantity of virus. Fortunately, large quantities of purified virus are not necessary for electron microscopy, serology, or microchemical tests. The ability to separate low concentrations may be an advantage if the separation is a prelude to analyses or determination of sedimentation coefficients, particularly in systems where interactions and deviations from the ideal become pronounced at higher concentrations. In general, density gradient centrifugation is most useful if it is considered not as a substitute for other methods of purification and centrifugation, but rather as an additional method to complement other techniques.
*
Published with the approval of the Director as Paper No. 993, Journal Series, Nebraska Agricultural Experiment Station. Cooperative investigations between the Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, and the Nebraska Agricultural Experiment Station.
Copyright © 1960 Academic Press Inc. Published by Elsevier Inc. All rights reserved.