162 



MICROSOMAL PARTICLES 



that in this concentration of versene (0.05 M), and at pH 9.0, less than 1 per 

 cent of the original magnesium should remain with the particles. 



The RNA/protein ratios of the dissociated components have been investi- 

 gated. The 60 and 40 S components were shown to be attacked and precipi- 

 tated by RNAase and protamine, indicating that they contain RNA. The 

 problem was then approached more quantitatively by comparing the ultracen- 

 trifuge patterns obtained by schlieren optics with those obtained by ultraviolet 

 absorption optics which measures the sedimentation of nucleic acid. It should 

 be noted that the concentration of particles in solutions employed for ultra- 

 violet absorption optics is 30 to 50 times lower than that used for schlieren optics. 

 In dilute solutions, the sedimentation coefficient will be higher and the reversi- 

 ble dissociation reaction will proceed further toward completion. Figure 6a 

 shows that all the nucleic acid moves as one component of 79 S in water. At 

 pH 7.5, 0.05 u, phosphate (fig. 6b), the particles are dissociated into two ultra- 

 violet-absorbing components of 37 and 59 S, those shown above to appear also 

 in the schlieren pattern. The absence of the 80 S particles, which do appear in 

 the schlieren pattern, in the ultraviolet absorption pattern in this phosphate 

 buffer is to be attributed to the complete dissociation of the original particles 



c 

 o 



o 



CO 



C) 



d 



o 



Fig. 6. Ultracentrifuge ultraviolet absorption patterns of particles under dissociating and 

 nondissociating conditions, (a) In water. Rotor speed 25, 980 rpm. (b) In 0.05 /x K-P0 4 , 

 pH 7.5, 0° C, for 1 hour. Centrifuged at 7.7° C. Rotor speed 37,020 rpm. (c) In 0.025 M 

 ETDA, pH 6.6, 0.025 p, K-P0 4 , 0° C, for 1 hour. Centrifuged at 6.2° C. Rotor speed 

 42,040 rpm. (d) In 0.7 M KC1, 0° C, for 1 hour. Centrifuged at 8.5° C. Rotor speed 

 37,020 rpm. 



