Density-Gradient Separations in the Ultracentrifuge

The general principles and some examples of density-gradient separation have been discussed by Charlwood (1966). The technique of using sucrose gradients (Pickels, 1943) to stabilize weak sedimenting boundaries has been furthered by Brakke (1951, 1953) and others. 

Density-gradient separations of cytoplasmic fractions from liver have been carried out to study the distribution of activity of several enzymes (Thomson, 1959). Ribosomes and polysomes have been fractionated to elucidate the mechanisms of protein synthesis (Watson, 1964), Various viruses have been studied with the density-gradient technique polio virus (Levintow and Darnell, 1960), Rous sarcoma virus (Crawford, 1960), Shope papilloma virus (Williams et ai, 1960), and adenoviruses (Allison et ai, 1960). Density-gradient fractionation has been particularly useful for separation of DNA molecules from various species of bacteria (Rolfe and Meselson, 1959) and from animal cells (Kit, 1961), Other types of molecules, e.g., antibodies, lipoproteins, and rheumatoid factor have been isolated by density-gradient methods [see Charlwood (1966) for examples]. 

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