4 J. Bracket 



amoebae, removal of the nucleus leads to considerable dis- 

 turbances of phosphorylation. 32p.incorporation into non- 

 nucleated halves slows down almost immediately (Mazia and 

 Hirshfield, 1950), while their ATP content undergoes an 

 increase in aerobiosis which probably reflects a block in the 

 utilization of the phosphate-bond energy of ATP (Brachet, 

 1955a). Under anaerobic conditions, on the other hand, non- 

 nucleated cytoplasm shows a markedly reduced ability for 

 keeping ATP in phosphorylated form (Brachet, 1955a). More- 

 over, the general metaboUc disturbance of non-nucleated cyto- 

 plasm is also revealed in other biochemical systems. As we 

 have shown (1955a), the utilization of lipid and carbohydrate 

 reserve products is considerably reduced in non-nucleated 

 halves of amoebae. 



These metabolic injuries can be accounted for, as we have 

 already suggested (Brachet, 1955a), by assuming that the cell 

 nucleus is involved in the synthesis of nucleotide coenzymes, 

 which are essential for glycolysis and cellular oxidations. 

 This hypothesis is in agreement with most recent findings. 

 Hogeboom and Schneider (1952) have shown that, in the liver, 

 the complete enzyme system for the synthesis of diphos- 

 phopyridine nucleotide (DPN) from ATP and nicotinamide 

 nucleotide is located in the nuclei. In the starfish oocyte, 

 as shown by our co-worker E. Baltus (1954), the same enzyme 

 system is concentrated in the nucleoli, which are fifty times 

 more active than entire oocytes in this respect. If one of 

 the biochemical functions of the cell nucleus consists in the 

 production of DPN-like nucleotide coenzymes, enucleation 

 should result in a rapid loss of these coenzymes from the 

 cytoplasm and Baltus (1956) has found that this is indeed the 

 case: the DPN content of fasted amoebae drops much faster 

 in the non-nucleated than in the nucleated halves. 



Certain conclusions can be drawn from these various results. 

 At first it appears that the presence of the nucleus is by no 

 means essential to keep up the normal rate of cellular oxida- 

 tions and that those cytoplasmic granules which are specially 

 active in cellular oxidations, in particular mitochondria, are 



