LYSOSOMES, A N KW (IROIP OF CYTOPLASMIC PARTlCLliS 



139 



100 



PERCENTAGE OF 

 MAXIMUM ACTIVITY 



NUMBER OF TIMES FROZEN AND THAWED 



12 



16 



Fig. 8. Activation of mitochondrial and lysosomal enzymes by freezing and thawing. Washed 

 mitochontlrial fraction frozen in dry ice-acetone mi.xture and thaweil number of times indicated 

 in abscissa. Anahtical techniques as in figure 7. 



in preparations of intact particles and is not solubilized by most of the treatments 

 which release the lysosomal hydrolases. In our experiments, its distribution pat- 

 tern differed significantly from those of the hydrolases and we were led to con- 

 clude that uricase is ". . . attached either to the insoluble framework of lyso- 

 somes or to a fourth distinct group of granules with the properties of large micro- 

 somes" (29). The difficulty involved is illustrated by a comparison of figures 3-4 

 and 5-6. According to the former, the frequency curve of sedimentation constants 

 is practically the same for uricase and for acid phosphatase. On the other hand, 

 their density distribution curves in sucrose-heavy water solutions (figs. 5 and 6) 

 differ to a remarkable extent and suggest the existence of a special group of 

 uricase-containing particles. Of interest in this respect are the recent findings by 

 Thomson and Klipfel (97) that the distribution of catalase is very similar to that 

 of uricase. 



To conclude this lengthy discussion, an additional word must be said concerning 

 the postulate of homogeneity. This postulate has been used as a working hypothe- 

 sis, and even when verified experimentally, can obviously be true only in first 



