78 



S. S. COHEN 



of different metabolic activities on the same material at the same time to 

 permit conclusions concerning their interrelations and significance for 

 nuclear metabolism. One may wonder whether the large requirement for 

 vitamm C is not related to the existence of a special mechanism necessary 

 for disposing of this possible receptacle of nuclear hydrogen transport. It is 

 conceivable that, in addition to an oxidative disposal of this compound to 

 oxalate, reduced ascorbate may be imphcated both in the solubilization of 

 the mitotic apparatus by converting disulfide bonds to — SH groups and 

 subsequently in the reductive generation of deoxyribonucleotides from 

 ribonucleotides during interphase. 



10 



z 0-8 



c 



■(D 

 O 



O.0-6 



CD 



^ 0-4 

 0-2 



' 1 r- 



- Mitosis 





40 42 45 50 60 



Bud length (mm) 



70 



80 90 100 



Fig. 10. Concentration of thiols in relation to nuclear division in Lilium Imigiflorum 

 (Stem, 1956). Solid line represents total soluble thiols; the broken line, reduced soluble 

 thiols. Bud length has been shown to be an index of cell development. 



That glutathione and ascorbate may fulfill a critical role in nuclear meta- 

 bohsm might also be inferred from the fact that nutritional requirements for 

 glutathione and ascorbate among microorganisms are quite rare, suggesting 

 that mutation to auxotrophy for these substances might be lethal. Unfulfilled 

 glutathione requirements in Glomerella are reported to lead to chromosome 

 abnormalities (Markert, 1952) and ascorbate deficiencies lead to blocks in 

 DNA synthesis (Sokoloff ef al, 1955). 



As noted earlier, isolated thymus nuclei can phosphorylate adenylic acid 

 to ATP (Osawa et al., 1957). This reaction is blocked by cyanide, azide, and 

 dinitrophenol, compounds wliich do not affect glycolysis but do typically 

 affect respiration and oxidative phosphorylation in mitochondria. Neverthe- 

 less, a number of reagents, e.g., dicumarol, and methylene blue, which block 



