160 



MICROSOMAL PARTICLES 



at the same concentration has also been found to have protective properties. 

 Similar results have been obtained for yeast particles [4]. 



The dissociation of particles to smaller subunits is a relatively rapid process. 

 Thus, essentially the same proportions between 80, 60, and 40 S components 

 are obtained in runs on materials incubated at 0° C in phosphate buffer, pH 

 7.5, 0.05 |j, for 2 minutes or for 16 hours. No evidence was found in these ex- 

 periments to suggest that the 60 and 40 S components are formed by aggre- 

 gation of smaller products. 



In concentrated potassium chloride solution (0.35 to 0.7 M), the particles 

 also dissociate into 60 and 40 S (fig. Ab, e) subunits, and this process too is sub- 

 stantially reversible (fig. 4&, c). Addition of magnesium chloride (0.015 to 



KCI 0.7M 



(a) 



(b) 



(c) 



Nyy 



(d) 



(e) 



Fig. 4. Ultracentrifuge patterns of particles in KCI solutions, (a) In 0.7 M KCI, 24° C, 

 for 30 minutes. Rotor speed 35,600 rpm. (/>) In 0.7 M KCI, 0° C, for 1 hour. Centrifuged 

 at 7° C. Rotor speed 42,040 rpm. (c) Solution of (b) dialyzed in 0.025 fi K-P() 4 , pH 6.5, 

 MgChl X 10" 3 M, 2-4° C, for 14 hours. Centrifuged at 6.8° C. Rotor speed 42,040 rpm. 

 (d) In 0.7 M KCI with 0.015 M MgCh, 0° C, for 1 hour. Rotor speed 35,600 rpm. (<?) In 

 0.35 M KCI, 0° C, for 1 hour. Rotor speed 35,600 rpm. 



