SITES WITHIN THE CELL 49 



could be partly solved by studying protein synthesis in certain types of cells 

 which can easily be cut into two parts, one of which is devoid of nucleus. 

 The enucleate fragments survive for some time and it is possible to 

 establish directly whether protein synthesis can take place in the absence of 

 a nucleus. 



Amoeba proteus was used by Brachet (1955) and by Mazia and Prescott 

 (1955) for such experiments. The nucleus of this Amoeba is usually located 

 in the rear part of the cell when the animal is moving about on a glass 

 surface. When the cell is cut into two approximately equal parts by means 

 of a thin glass rod, the fragment which contains the nucleus retains all 

 the morphological characters and the habits of a normal Amoeba. Nucleate 

 fragments thrust out pseudopodia, crawl about and catch ciliates or other 

 prey upon which they feed. To the contrary, enucleate moieties are rather 

 inert; they assume a nearly spherical shape shortly after sectioning, lose 

 the ability to form pseudopodia and to secure food. Actually, enucleate 

 amoeba fragments are always starved; they survive nevertheless for 10-14 

 days, before collapsing. In all the experiments with Amoeba fragments, the 

 nucleate part to which the enucleate halves are compared must naturally 

 also be deprived of food. 



Starvation is definitely not favourable to protein synthesis. In spite 

 of this, it was possible to obtain very interesting information on the 

 presently discussed question with this material. As can be expected, the 

 total amount of protein decreases in starved Amoeba. Brachet (1955) 

 observed that total protein diminishes more rapidly in enucleate fragments 

 than in starved whole Amoeba or in starved nucleate fragments. By follow- 

 ing, in the course of time, the changes in several individual enzymes in 

 both types of fragments, Brachet showed that the removal of the nucleus 

 results in widely difi'erent effects in the case in the individual enzymes 

 studied. 



Thus an acid phosphatase, a dipeptidase and an esterase decreased much 

 faster in enucleate fragments than in nucleate parts, but other enzymes, 

 like a protease, enolase, adenosine triphosphatase and the respiratory 

 system were not more labile in the absence of the nucleus than in its 

 presence during starvation. It would seem therefore that the maintenance 

 of the individual cytoplasmic proteins is not equally dependent on the 

 presence of the nucleus (Brachet, 1955, 1956, 1957). 



Although a net decrease of protein material is always observed in starved 

 Amoebae, some anabolic processes can nevertheless be observed. Mazia and 

 Prescott (1955), Mazia (1956), Ficq (1955) and Brachet and Ficq (1956) 

 showed that labelled methionine or phenylalanine are incorporated into 

 cytoplasmic proteins. The incorporation is 50 per cent lower in enucleate 

 fragments than in nucleate moieties or in intact Amoebae. However re- 

 duced, the incorporating capacity is maintained for up to 10 days after 



