STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 77 



of many kinds of normal cells in tissue culture and their apparent trans- 

 formation to new types. Furthermore, it would be important to know the 

 effects of tumor viruses on these metabolic systems. 



Despite the presence of typical glucose-utihzing systems in nuclei with 

 accompanying oxidation-reductions involving DPN and TPN, it is a mystery 

 how hydrogen and electron transport continue in this cellular structure. 

 Liver nuclei do not contain flavoproteins, cytochrome c, and cytochrome 

 oxidase, and no mechanism is known in this organelle for the transfer of 

 hydrogen to molecular oxygen. According to Schneider and Hogeboom 

 (1956), FAD pyrophosphorylase does not exist in nuclei despite the con- 

 centration of DPN pyrophosphorylase and UDPG pyrophosphorylase (Smith 

 and Mills, 1954). Stern and Timonen (1954) detected very small amounts of 

 DPN-cytochrome c reductase and of flavin in calf thymus nuclei, amounts 

 which they attributed to contamination. They have suggested that coenzyme 

 reoxidation requires the participation of cytoplasm, since calf thymus nuclei 

 contain 60 % of the total cell mass and enzymes capable of half of the 

 glucose-6-phosphate metabolism of this cell. 



In studies of nuclear glutathione, the concentration of which is relatively 

 high, they found glutathione reductase in the amount of 16 to 20 % of that 

 in cytoplasm. Ascorbic acid was also found in nuclei, but these investigators 

 considered it unlikely that these substances actually participate in a major 

 pathway of hydrogen transport. 



Actually one could conceive that these latter systems are precisely those 

 involved in the chain of electron transport required in this orgenelle, as in the 

 following sequence of reactions: 



DPNH -f TPN+ > TPNH + DPN + 



2TPNH 4- oxidized glutathione (GSSG)-> 2 reduced glutathione (GSH) + 2TPN + 

 2GSH + dehydroascorbate > GSSG -}- ascorbate 



Keduced glutathione generated during metabolism of glucose-6-phosphate 

 might participate in the generation of sulfhydryl groups essential to the 

 development of a mitotic spindle and nuclear division, as described by 

 Rapkme (1931), Mazia (1956), and Stern (1956). The generation of soluble 

 GSH prior to mitosis in Lilium is presented in Fig. 10. The cyclic production 

 of acid in dividing sea urchin eggs has imphcated glycolysis in division 

 (Brachet, 1950), and a classic inhibitor of glycolysis, sodium fluoride, blocks 

 prophase in mitosis (Hughes, 1952). Furthermore, ascorbate concentration 

 also rises during mitosis of microspores in Lilium (Stern and Timonen, 1954), 

 whereas Og consumption falls (Erickson, 1947). 



It is premature to make much of this apparent concatenation of events. 

 One may note, for example, that Holter and Zeuthen (1957) have reported 

 that, in sea urchin development, Og consumption is maximal at prophase 

 and falls thereafter. It will be necessary to have many of these measurements 



