LYSOSOMES, A NEW CROIP OF CYTOPLASMIC PARTICLES 



135 



0.5 



FREQUENCY x 10 



-9 



URICASE 



ACID PHOSPHATASE 



CYTOCHROME 



OXIDASE 



- GLUTAMIC 

 DEHYDROGENASE 



SECONDS X 10' 



Fig. 4. Distribution curves <if scciinicntation constants. Constructed by derivation of the 

 sedimentation diagrams of figure 3, according to de Duve et til. (25). The sethmentation con- 

 stant J" applies to 0.25 m sucrose at 0°. 



sedimentation diagram of protein (fig. 3) sliovvs no sign of being bimodal. This, 

 however, we believe to signify that the phosphatase particles are associated with 

 a very small proportion of the total protein of the preparation; in other words, 

 that they are much less numerous than mitochondria. 



The association of acid phosphatase with a special group of particles thus rests 

 on a firm experimental basis. That the other hydrolases belong to the same gen- 

 eral group is made obvious by our previous results and by those of figures 3 

 and 6. However, these results also make it clear that the lysosomal enzymes do 

 not obey the postulate of homogeneity as closely as do the mitochondrial or 

 microsomal enzyiTies which have been similarly studied. At present, the situation 

 may be summed up as follows: the release of all lysosomal enzymes occurs in 

 an almost perfectly parallel fashion; hut their distribtitions, whether determined 

 on the basis of sedimentation rate or of density, are not identical. Either, there- 



