Purification of Chloroplasts by a Density Technique.

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Abstract
When an impure preparation of chloroplasts of spinach, kidney bean or tobacco is suspended in fluid of density 1.13 or over and centrifuged, it is found that some chloroplasts float to the top in a relatively pure state, while the remainder of the chloroplasts and contaminating materials sediment to the bottom. The purity of the floating chloroplasts is established by a number of chemical criteria. Fluid density is altered by using varying concentrations of glycerol and sucrose. Very small non-chloroplast particles will also float; but these can be removed by a preliminary differential centrifugation. Chloroplasts from young leaves do not float as readily as mature leaf plastids. Limitations and uses of the method are discussed.