Nuclear control of enzymatic activities 



composition; work on homogenates, especially, is unreliable when one is using very 

 small amounts of material, as is the case with fragments of Amoeba. It is to be hoped 

 that improvements in the techniques of homogenization and centrifugation will 

 make a quantitative investigation on homogenates of amoebae possible. 



What is, however, feasible is a study of the enzymatic composition of nucleated 

 and non-nucleated halves (Brachet, 1952a; Urbani, 1952a, 19520): two of the en- 

 zymes studied so far, esterase and acid phosphatase, are present in large amounts in 

 the microsomes, in the case of the mammals at any rate. Three other enzymes, 

 adenosinetriphosphatase, amylase, and protease have been followed simultaneously: 

 the first is bound mostly to mitochondria in rat liver, while the other two are present 

 in the large granules of the amoebae (Holter and Pollock, 1952; Holter and Lovtrup, 

 1949). Finally, we studied also dipeptidase, as this enzyme, according to Holter and 

 Lovtrop, (1949), is soluble and is thus apparently not bound to any type of cyto- 

 plasmic granules. 



These experiments have yielded perfectly clear results: while the 'mitochondrial' 

 enzymes (adenosinetriphosphatase, amylase and protease) are completely unaffected 

 by the removal of the nucleus, even after 1 2 days, the 'soluble' dipeptidase behaves 

 like total proteins: after an initial drop, the amount remains constant in non- 

 nucleated halves. Finally, the enzymes which are presumably bound to the micro- 

 somes (acid phosphatase and esterase) behave exactly like RNA: only after the third 

 day after bisection of the amoebae does their amount decrease in the non-nucleated 

 half, but this drop is so pronounced that, on the twelfth day, only 20-30 per cent, of 

 the initial amount is still left. 



These findings make it likely that the control exerted by the nucleus on the 

 various cell proteins largely depends on their intracellular distribution : negligible in 

 the case of mitochondria, nuclear control is weak for soluble proteins and very im- 

 portant for microsomes, which probably disappear rather rapidly in the absence of 

 the nucleus. 



Such a view is rather different from the hypothesis of E. B. Wilson (1925) : none of 

 the enzymes we studied are accumulated in the nucleus and there is no evidence 

 that they are synthesized in the nucleus itself. Nuclear control of enzymatic activities 

 is obviously much more complex than was expected, as various proteins behave very 

 differently after removal of the nucleus. 



The nucleus and the production of coenzymes 



It should first be emphasized that none of the enzymes we have studied are present 

 in the nucleated fragments in much larger amount than in the non-nucleated half: 

 none of them is therefore predominantly accumulated in the nucleus. We know, 

 however, from work on homogenates that the enzymes which catalyse the synthesis 

 of nucleotides, including various coenzymes, are on the contrary concentrated in 

 the nuclei (Stern et al., 1952; Hogeboom and Schneider, 1952).* 



Technical difficulties have unfortunately prevented us so far from studying these 

 interesting enzymes; but some of the results we have obtained on fragments of 



* Recent unpublished experiments in this laboratory (E. Baltus) have shown that nucleoli isolated from 

 starfish ovocytes are very rich in nucleosidephospborylase, but contain little guanase or adenosinedeaminase. 

 The enzyme which catalyses the synthesis of diphosphopyridinenucleotide is also accumulated in these 

 nucleoli. 



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