TS'O 163 



into the 59 and 39 S components at the low concentration. The ratio of the 

 amounts of ultraviolet-absorbing material, i.e., nucleic acid, contained in the 

 59 and 39 S boundaries is similar to the ratio of amounts of material contained 

 in the two boundaries as observed with schlieren optics. These ratios are ap- 

 proximately 2.3 : 1. Treatment with EDTA results in nucleic acid-containing 

 components of 24 and 44 S (fig. 6c) as were likewise observed by schlieren 

 optics (fig. 5b). The ratio of the amounts of nucleic acid in the two compo- 

 nents is similar to the ratio of the amounts of material contained in the two 

 boundaries as observed in schlieren optics, namely, 2:1. The pattern of the 

 particles incubated in 0.7 M KC1 and observed with absorption optics (fig. 6d) 

 is, however, markedly different from that observed with schlieren optics (fig. 

 4£). Components of 75 and 58 S which are observed with schlieren optics are 

 not observed with absorption optics. In the latter case, however, a new bound- 

 ary of component 23 S is present to the extent of about 40 per cent of the 43 S 

 component. The probable explanation of this behavior is that, at the low con- 

 centration necessary for the employment of ultraviolet optics, the 80 S and the 

 59 S particles are further dissociated to an undetectable concentration and a new 

 component of lower sedimentation appears. The 24 S component observed 

 with ultraviolet optics in potassium chloride-treated preparations is presumably 

 similar to or identical with the 25 S component observed in solutions treated 

 with EDTA. Thus, the original particles and their dissociation products all 

 have similar ratios of ultraviolet-absorbing material to mass. 



The intrinsic viscosity of microsomal particles in media which promote dis- 

 sociation was studied in order to find out what over-all changes in frictional 

 coefficient are attendant upon dissociation. These experiments were performed 

 in versene and in potassium chloride solutions at low temperature since at 

 higher temperature the system in versene aggregates and the system in potas- 

 sium chloride shows evidence of ribonuclease action. Even though particle 

 preparations were clarified twice by low-speed centrifugation, the possibility 

 of the presence of small amounts of aggregates cannot be excluded. The in- 

 trinsic viscosity of the microsomal particles in phosphate buffer was found to 

 be 0.11 (100 cc/g) (fig. la), identical with the value found for 24° C. In water, 

 the value was 0.12/100 cc/g, an increase which may be due to the electroviscous 

 effect. In solutions of dissociated particles in versene at p¥L 6.8 and 9.0, and in 

 potassium chloride (fig. lb, c, d), a slightly higher value of reduced viscosity 

 was obtained at high concentration. The intrinsic viscosity of these solutions, 

 however, was again found to be 0.11 to 0.12. Thus, no change in intrinsic 

 viscosity is observed upon dissociation of the particles. The most reasonable 

 explanation for this result is that the units of 60, 40, and 25 S have the same 

 frictional coefficient as the 80 S particles. 



The above experiments on the dissociation of the 80 S particles can be sum- 

 marized as follows: 



1. When magnesium and calcium are removed from microsomal particles 

 (79 to 81 S), three ultracentrifugally identifiable components are obtained as 



