ROBERTS, BRITTEN, AND BOLTON 



87 



^Totol C«M eitroct 



AaJVw^>?V 



\ .,100,000 g SN 



50 



100 

 Eluting fluid, ml 



150 



Fig. 3. Elution patterns of total cell juice and supernatant fluid of 100,000^ 2-hour spin. 

 Upper curve, optical density at 254, indicating nucleic acid concentration; lower curve, 

 S 35 radioactivity, indicating protein. Note nucleoprotein peak which is missing in 100,00% 



SN. 



is partly nucleoprotein and partly due to free DNA and RNA which still re- 

 main in the 100,000^ supernatant fluid. 



The elution pattern is not sensitive to the size of the particles. The same pat- 

 tern is obtained whether the microsome pellet is composed mostly of the large 

 (80 S) particles or of the smaller 20 to 40 S particles that result from magne- 

 sium deficiency. Compare figures 4# and b. 



Microsome pellets when resuspended and analyzed on the column show the 

 nucleoprotein peak together with a quantity of other protein which depends on 

 the method of preparation (fig. 4). A part of the contamination of the micro- 

 some pellet is due to small bits of cell wall, and another part is due to nonpar- 

 ticulate protein. In 2 hours at 100,000^ roughly 70 per cent of the 3-galac- 

 tosidase is sedimented. See also Dagley and Sykes [5, 11]. Accordingly the 

 least-contaminated preparations of ribosomes are those obtained by resuspend- 

 ing a microsome pellet and centrifuging again in the swinging bucket head 

 (fig. 4c). 



Unfortunately the column cannot be used to prepare purified ribosomes be- 

 cause the material eluted from the column is quite different from that origi- 

 nally adsorbed. When the fractions containing the nucleoprotein peak are 



