78 



MICROSOMAL PARTICLES 



0.001 M MgCl 2 , and 0.01 M KC1). After vacuum nitration through celite filter- 

 aid, the microsomes were sedimented from the filtrate by ultracentrifugation in 

 the preparative ultracentrifuge (Spinco Model L) at 114,000g (40,000 rpm) for 

 1 hour. The translucent microsomal pellets isolated from yeast cells in different 

 growth stages were carefully redissolved in the buffered solvent and analyzed 

 in the analytical ultracentrifuge (Spinco Model E) at 200,000^. Figure 2 shows 



(«) 



(c) 



GO 



Fig. 2. Sedimentation photographs of microsome particles from yeast-cell extracts 

 6 minutes after up to speed (UTS) at 200,000,? in the analytical ultracentrifuge (Spinco 

 Model E). (a) Top: Cell extract from 48-hour nitrogen-starved cells corresponding to the 

 inoculum cells at time 0. Bottom: Extract from nitrogen-starved cells 1.5 hours after cells 

 given utilizable nitrogen, (b) Top: After 3 hours. Bottom: After 5 hours, (c) Top: 

 10 X concentrated extract from nitrogen-starved cells 7 hours after cells given utilizable 

 nitrogen. Bottom: Extract from nitrogen-starved cells 10 hours after cells given utilizable 

 nitrogen, (el) Top: After 26 hours. Bottom: After 52 hours. 



