Nuclear control of enzymatic activities 



Mirsky (1952) is definitely accumulated in these nuclei, has an almost even distri- 

 bution in both halves of Amoeba, even 11 days after bisection. 



This negative result leads us to believe that the nucleus plays a part in the activa- 

 tion of glycolytic enzymes, by the production of the necessary coenzymes, rather 

 than in their actual synthesis. Further work will of course be required to decide on 

 which step the nucleus is acting; the fact that glycogen is involved and that phosphate 

 penetration is reduced in non-nucleated halves seems to point towards the phosphory- 

 lase system, which requires for full activity — besides the protein — adenylic acid, 

 -SH groups, and inorganic phosphate. 



It is worth mentioning that decreased capacity to keep ATP in the phosphory- 

 lated form during anaerobiosis and reduced utilization of glycogen might very well 

 prove to be biochemical abnormalities characteristic of any cell the nucleus of which 

 is severely altered: these very same metabolic troubles have already been found in 

 strongly lethal interspecific frog hybrids (Barth and Jaeger, 1947; Gregg, 1948), as 

 well as in frog eggs fertilized with nitrogen-mustard-treated sperm (unpublished 

 experiments). 



PROTEIN SYNTHESIS IN THE ABSENCE OF THE NUCLEUS IN ACETABULARIA 



The very important finding of Hammerling (1934), that a non-nucleated piece of 

 Acetabularia is capable of considerable growth and regeneration when light is supplied, 

 has been confirmed and extended by our co-worker F. Vanderhaeghe (1952): her 

 quantitative measurements of the dry weight and the total nitrogen content of 

 nucleated and non-nucleated fragments have shown that growth and protein 

 synthesis proceed at the same rate in both halves during 2-3 weeks; they then fall 

 off considerably in the enucleate fragments. 



This decrease in the potentiality for growth and regeneration after 2-3 weeks 

 has also been shown in simple experiments by Brachet and Brygier (1953) : if non- 

 nucleated halves are placed in the light immediately after the bisection, 50 per cent, 

 of them soon produce umbrellas ; the same proportion of umbrellas is obtained even 

 if the fragments have been left in the dark, where neither growth nor regeneration 

 occurs, for 1 or 2 weeks prior to illumination; but when the non-nucleated halves 

 are kept for 3 weeks in the dark before illumination, only 15 per cent, form umbrellas. 

 Finally, when these non-nucleated pieces are left for 4 weeks in darkness, no 

 umbrellas are produced in the light afterwards. 



Biochemical experiments with 14 CO a (Brachet and Chantrenne, 1951) have 

 entirely confirmed these biological findings: incorporation of 14 C0 2 in the proteins 

 (carboxylic group of the amino-acids) is identical in both nucleated and non-nucleated 

 fragments at the beginning, but it drops in the non-nucleated halves after 2-3 

 weeks and thereafter falls steadily. Incorporation of labelled C0 2 in the proteins of 

 Acetabularia only occurs in the light and in the proteins of the chloroplasts (Brachet 

 and Chantrenne, 1951) ; if glycine- 14 C instead of 14 CO a is used as a precursor, it is 

 incorporated in the proteins in the dark as well as in the light, and the microsomes 

 are now more active than the chloroplasts (Brachet and Brygier, 1953). The alga 

 thus possesses two different mechanisms of protein synthesis, according to the ex- 

 perimental conditions; such a finding is not without interest since it is known from 



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