120 ROLE OF THE CELL NUCLEUS 



number of enzymes in regenerating fragments oi Acetabularia. They 

 found that two enzymes involved in glucidic metaboUsm, like aldo- 

 lase, are synthesized at the same rate as the total proteins ; these en- 

 zymes are phosphorylase and fructosidase. On the other hand, they 

 found a drop in acid phosphatase in regenerating enucleate frag- 

 ments. It is interesting that this enzyme shows a strongly decreased 

 activity after removal of the nucleus in Amoeba as well as in Acetab- 

 ularia. It might be that acid phosphatase (and perhaps esterase) is 

 synthesized in the nucleus itself or that the latter produces a sub- 

 stance which is absolutely necessary for the synthesis of this enzyme. 

 It might also be that, in Acetabularia, the glycolytic enzymes which 

 undergo synthesis in the absence of the nucleus are mainly localized 

 in the chloroplasts, while acid phosphatase would be more closely 

 linked to the microsomes. Such an explanation would be in con- 

 formity with the above-mentioned results of Naora, Brachet and 

 Naora (1959) on the behaviour of chloroplastic and microsomal 

 RNA's in regenerating enucleate fragments of Acetabularia. Ob- 

 viously, a good deal more experimental work is required before a 

 definite answer can be given to these intriguing questions. 



The enucleate cytoplasm is thus still capable of synthesizing 

 enzymes, that is, specific proteins. One would very much like to 

 know whether induced enzyme synthesis is still possible in the 

 absence of the nucleus. Unfortunately, the experiments designed to 

 test that possibility (Brachet et ah, 1955) have not led to definite 

 results. While an increase in catalase activity was found many times 

 when enucleate pieces of Acetabularia were cultivated in the pres- 

 ence of hydrogen perodixe, it was impossible to repeat the results in 

 later experiments. The reasons for this lack of uniformity in the 

 results remain unknown; it might simply be due to bacterial 

 contamination in the first series of experiments. 



We have suggested before that the nucleus might successfully 

 compete with the cytoplasm for RNA precursors. The same possi- 

 bility exists for protein synthesis and there is even some evidence 

 in its favour. It has been reported by Giardina (1954) and con- 

 firmed by Brachet et al. (1955) that the proportion of acid-soluble 

 nitrogenous compounds, compared to protein nitrogen, increases 



Text continued on p. 124 



