Cytoplasmic & Nuclear Structure & Metabolism 9 



anucleate cytoplasm cannot keep up its normal ATP content 

 for long. We already know that these non-nucleated fragments 

 rapidly lose the ability to utilize stored glycogen (Brachet, 

 1955a). Similarly they stop incorporating ^^P (Mazia and 

 Hirshfield, 1950) and cannot maintain a normal DPN content 

 (Baltus, 1956). This leaves no doubt that the loss of the nucleus 

 leads to serious defects of the metabolism of carbohydrates 

 and phosphorylated compounds. A logical consequence of 

 such an inhibition of the energy-providing mechanisms of 

 the cell would be a severe disturbance of protein synthesis, 

 since it is well established that the synthesis of proteins or 

 even of simple peptide bonds requires energy from the high 

 energy phosphate bonds of ATP (Borsook, 1950; Siekevitz, 

 1952; etc.). 



With respect to protein synthesis, removal of the nucleus 

 brings into play an additional unfavourable factor in the 

 amoeba: we have already mentioned that RNA is also in- 

 volved in this synthesis. Removal of the nucleus, as shown 

 in 1951 by Linet and Brachet and, in confirmation, by 

 James (1954), leads to an immediate and marked fall in the 

 RNA content of cytoplasm (this can reach 70 per cent within 

 ten days). Such a drop in cytoplasmic RNA is, of course, in 

 agreement with the more recent autoradiograph experiments 

 of Goldstein and Plant (1955), showing that at least some of 

 the cytoplasmic RNA in amoebae is of nuclear origin. It is 

 not surprising that total protein content decreases faster in 

 non-nucleated than in nucleated halves (Linet and Brachet, 

 1951). 



Given the conditions of our experiments (complete fasting), 

 one could not, of course, expect net protein synthesis to occur. 

 A process very near to it could be followed, however: the 

 incorporation of tagged amino acids into proteins. In a 

 recent paper, Mazia and Prescott (1955) have shown that 

 removal of the nucleus leads, within as little as 2 or 3 hours, 

 to a drastic decrease in the uptake of radioactive methionine 

 by the proteins of non-nucleated amoebae. The N/A ratio 

 (N = nucleated half; A = anucleate half) is already increased 



