Nuclear control of enzymatic activities 



EXPERIMENTAL RESULTS 



The nucleus and cellular oxidations 



It is a well-known fact that non-nucleated halves of Amoeba soon round up and 

 become incapable of normal feeding; in order to place nucleated and non-nucleated 

 fragments in similar experimental conditions, it is necessary to leave both of them 

 without external food supply during the whole experimental period. Under these 

 conditions, nucleated halves survive three weeks and non-nucleated ones seldom live 

 more than a fortnight. 



Measurements of the oxygen consumption, made every other day on nucleated 

 and non-nucleated halves of Amoeba, have shown that the respiration of both types 

 of fragment remains identical for at least ten days, if the values are corrected for the 

 differences in size of the pieces (Brachet, 195 1 ) . 



Similar results have been obtained in the case of Acetabularia mediterranea (Chan- 

 trenne-Van Halteren and Brachet, 1952), where non-nucleated halves can survive 

 up to five months : even three or four months after sectioning, non-nucleated pieces 

 still respire at the same rate as the nucleated ones, provided the results are expressed 

 in terms of dry weight. 



These results are in good agreement with those we had obtained earlier (1939) 

 when studying the oxygen consumption of isolated nuclei (germinal vesicles) from 

 frog's oocytes; they also agree with the findings of Shapiro (1935) on the respiration 

 of nucleated and non-nucleated halves of unfertilized sea-urchin eggs : in neither 

 case does the cell nucleus play a leading role in cellular oxidations, as was believed 

 by Loeb (1899). 



When the oxygen consumption of cells which have been ultra-centrifuged in the 

 living condition is studied, it is found that the main respiratory enzymes are actually 

 bound to large cytoplasmic granules, comparable or identical with the mitochondria : 

 this conclusion can be drawn from the experiments of Ballentine (1939) on unfertil- 

 ized sea-urchin eggs, of Huff and Boell (1936) on Ascaris eggs, and of Chantrenne 

 (1944) on frog's liver. 



It is therefore obvious that the nucleus cannot be the main centre of cellular 

 oxidations and that Loeb's theory is no longer tenable; work on intact cells or 

 organisms entirely confirms the results obtained on homogenates in showing that 

 large cytoplasmic granules, presumably the mitochondria, contain the more im- 

 portant respiratory enzymes. Furthermore, the work done on unicellular organisms 

 clearly shows that these mitochondria are very largely independent of the presence 

 or the absence of the nucleus for normal functioning. 



Ribonucleic acid [RNA), proteins and glycogen 



We have already seen that RNA is mostly found in the small cytoplasmic granules 

 (microsomes), as well as in the nucleoli, and that this substance is supposed to play 

 some important role in protein synthesis (Caspersson, 1941 ; Brachet, 1941). 



In amoebae, both cytochemical techniques (Brachet, 1950) and quantitative 

 micro-estimations (Linet and Brachet, 1951) have clearly shown that the removal of 

 the nucleus is followed by a considerable drop in the RNA content of the cytoplasm : 

 3 days after sectioning, non-nucleated halves become poorer in RNA than the 



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