106 ROLE OF THE CELL NUCLEUS 



question : are all the cytoplasmic proteins of the Amoeba equally 

 dependent on the nucleus ? 



This was studied (Brachet, 1955) by following, over a period of 

 time, the changes of various enzymes (hence of as many specific 

 proteins) in both types of fragments. The experiments showed that 

 the removal of the nucleus results in widely different effects in the 

 case of different enzymes. Some of them, like protease, enolase and 

 adenosine triphosphatase, remain practically unchanged after the 

 removal of the nucleus. Amylase (Urbani, 1952) behaves in much 

 the same way, except for an unusual initial increase in activity in 

 the enucleated halves. Dipeptidase, on the other hand, shows an 

 initial decrease and then remains essentially constant. Acid phos- 

 phatase and esterase practically disappears from the enucleated 

 cytoplasm after a few days. These experiments establish beyond 

 doubt that different enzymes are placed under nuclear control to 

 different extents and that this postulated "control" of the nucleus 

 is much more complex than might have been expected. It should be 

 noted that none of the enzymes studied ever showed a predominant 

 nuclear localization, a finding which disposes of Wilson's (1925) 

 theory of nuclear storage or synthesis of enzymes. 



The reason for this strikingly different behavior of the various 

 enzymes that we studied remains uncertain. It is tempting to spe- 

 culate that the cellular localization of the different enzymes is of 

 importance in this respect. As shown by Holter (1954, 1955), amyl- 

 ase and protease are bound to large granules in the Amoeba (mito- 

 chondria or the lysosomes of De Duve et al. (1955)). This might 

 imply that mitochondria largely escape nuclear control, as indicated 

 by the experiment made of the effects of enucleation on the respi- 

 ration of amoebae. The different behavior of dipeptidase is not 

 surprising since, according to Holter (1954), this ubiquitous enzyme 

 is probably in solution in the hyaloplasm. Acid phosphatase and 

 esterase, which behave like RNA, might be bound to microsomes. 

 But this interpretation of the findings is weakened by Holter's 

 (1955) more recent report that acid phosphatase behaves like pro- 

 tease : it is normally bound to large granules and is released in solu- 

 tion on homogenization. Protease, amylase and acid phosphatase 



