Density gradient centrifugation for

Figure 13.7 Caesium chloride density gradient centrifugation for (a) the separation of DNA from RNA and protein and (b) the separation of linear DNA and supercoiled DNA.

The presence of yet another class of turtle immunoglobulin, intermediate in size between 7 S and 19 S, is suggested by the investigation of Coe, who employed density gradient centrifugation for separating immunoglobulins of different sizes (85). 

Heavy isotopes endow the compounds in which they appear with slightly greater masses than their unlabeled counterparts. These compounds can be separated and quantitated by mass spectrometry (or density gradient centrifugation, if they are macromolecules). For example, O was used in separate experiments as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from HgO, COg, or both ... 

The microsome fractions see Fig. 1) that were prepared from mulberry cortical parenchyma cells were fractionated to 24 or 25 fractions using the 15-50% sucrose linear density gradient centrifugation see Fig. 2). Profiles of the marker enzymes and the protein content are described in Fig. 3. In general, the antimycin A-insensitive cytochrome c reductase activity is exhibited at a lower density than are those of the marker enzymes. The fraction that exhibited the highest antimycin A-insensitive cytochrome c reductase activity for each month was used as the ER-enriched fraction. 

PF had been proposed as the terminal complex (23) and associated pores were reported on the outer membrane EF (24). Due to their proximity to the site of cellulose ribbon extrusion from the cell surface, these structures were assumed to be responsible for cellulose synthesis. A model was advanced in which cellulose synthase was localized on the outer membrane, which invoked adhesion sites between the outer and plasma membranes as a mechanism to explain the transfer of uridine-diphosphoryl-glucose (UDPG) from the cytoplasm to the cellulose synthases (25,26). However, when the outer and plasma membranes of Acetobacter were isolated separately by density-gradient centrifugation, the cellulose synthase activity was localized only in the plasma membrane fraction (27). Therefore, the linear structures observed on the Acetobacter outer membrane, while they may be associated in some manner with cellulose biosynthesis, are probably not the cellulose synthase terminal complexes. Since no ultrastructural evidence for adhesion sites between the outer and plasma membranes has been presented, a thorough investigation of the mechanism of / (1-4) glucan chain translocation from the cytoplasmic membrane to the outer membrane in Acetobacter xylinvm is now in order. 

Rubidium chloride is used in preparing rubidium metal and many rubidium salts. Also, it is used in pharmaceuticals as an antidepressant and as a density-gradient medium for centrifugal separation of viruses, DNA, and large particles. Other applications are as an additive to gasoline to improve its octane number and as a catalyst. 

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