Cytoplasmic & Nuclear Structure & Metabolism 5 



largely independent of the nucleus. The latter, however, does 

 exert an indirect control by regulating these oxidation pro- 

 cesses through the synthesis of the nucleotide coenzymes. It 

 appears probable that these coenzymes are protected from 

 hydrolytic enzymes when bound to the mitochondria, in 

 which case removal of the nucleus can have little effect on 

 bound DPN and cannot interfere strongly with cellular 

 oxidations. On the contrary, free coenzymes, those not bound 

 to mitochondria, would appear to be left unprotected against 

 hydrolysis and this should result in a rapid drop of glycolysis 

 with an incomplete utilization of the stored glycogen after 

 removal of the nucleus. Thus non-nucleated cytoplasm, 

 I with its low content of free DPN and the resulting deficient 

 glycolysis, should no longer keep up its normal ATP content 

 in anaerobic conditions. 



Such a direct action of the nucleus might be postulated not 

 only for the synthesis of DPN, but also for that of the other 

 nucleotide coenzymes (triphosphopyridine nucleotide, flavine- 

 adenine dinucleotide, coenzyme A, etc.). The experiments to 

 prove it have yet to be done but it remains an attractive 

 hypothesis, in view of the extremely important part taken by 

 the nucleus in the metabolism of a polynucleotide, ribonucleic 

 acid (RNA). We already know from ^^P experiments by 

 Marshak (1948), Marshak and Calvet (1949), Jeener and 

 Szafarz (1950) and Barnum and Huseby (1950), that nuclear 

 RNA shows a much higher specific activity than cytoplasmic 

 RNA. Studies Vvdth other radioactive precursors such as 

 orotic acid (Hurlbert and Potter, 1952), glycine (Bergstrand 

 et al., 1948), formate (Payne et al., 1952; Smellie et al., 1953) 

 have confirmed these results. In all cases, incorporation by 

 nuclear RNA was very high, higher in fact than that by any 

 cytoplasmic fraction. 



There has been much debate as to whether, as suggested 

 by Jeener and Szafarz (1950), nuclear RNA is a precursor of 

 cytoplasmic RNA. Recent mathematical work by Barnum, 

 Huseby and Vermund (1953), as well as measurements show- 

 ing that nuclear and cytoplasmic RNA's have different 



