LYSOSOMIiS, A NEW (;K()l'P OF CYTOPLASMIC PARTICLKS 



'4' 



Fig. 9. Electron micrograph of lysosomc-rich fraction. Ultrathin section of purified pellet. 

 [From (66).] X 36,300. 



The final morphological identification of lysosomes must therefore await a 

 better purification of the particles. The following account of a recent experiment 

 performed by Beaufay may serve to illustrate the difficulties which attend this 

 problem. A mitochondrial fraction containing about 75 per cent of the total lyso- 

 somal enzymes and of uricase and 25 per cent of the total proteins of the homog- 

 enate was subjected to a fractionation in a gradient of sucrose in heavy water, 

 analogous to that of figure 6. From one gram of liver a minute dark-brown pellet 

 was obtained, which contained essentially no cytochrome oxidase, 10—15 P^'' '^^^^ 

 of the lysosomal enzymes, 35 per cent of the uricase and about 0.5 per cent of 

 the proteins of the fraction. In this pellet, therefore, the lysosomal enzymes were 

 purified 60- to 90-fold with respect to the homogenate, with a yield of about 10 

 per cent; and uricase more than 200-fold with a yield of 25 per cent. The material 

 was fixed in osmium tctroxide, at which stage it became almost invisible to the 

 naked eye; attempts to embed and section it proved unsuccessful. We are ob- 

 viously dealing here with what might be called 'trace organelles,' and their purifi- 

 cation for the purpose of identification may prove quite arduous. 



The dense bodies found in our fractions or seen around bile canaliculi in liver 

 preparations are fairly polymorphic. The simplest ones appear to be solid and 



