(Dounce, 1954), possibly of the type demonstrated by the AUfrey 

 group. The results of Allfrey and coworkers indicating that ATP synthe- 

 sis is coupled to oxidative processes in the nucleus, are interesting in the 

 light of the finding that isolated plant cell nuclei contain ascorbic acid 

 and glutathione but are lacking in flavoproteins and cytochrome c (Stern 

 and Timonen, 1954). It is conceivable that glutathione and ascorbic 

 acid, with their high capacity for oxidation-reduction, may form part 

 of an electron transport system operating in the nucleus which may in 

 some way be related to the aerobic synthesis of nuclear ATP. The cyclic 

 variations in ascorbic acid reported by Stern and Timonen (1954) to 

 occur during the mitotic cycle certainly merit further investigation. 



TABLE 6-1. Enzymes AbsenI from Isolated Nuclei.* 



Succinoxidase Choline oxidase 



Cytochrome oxidase L-Amino acid oxidase 



Catalase D-Amino acid oxidase 



Cytochrome c Proline oxidase 



Uricase Malic dehydrogenase 

 Xanthine oxidase 



" Data from Siebert, G. and Smellie, R. M. S., 1957. "Enzymatic and Metabolic 

 Studies on Isolated Nuclei," Intern. Rev. Cytology., 6, Table I, p. 391. 



Brachet (1957) has discussed in detail the results of Allfrey's group 

 and has suggested that the aerobic metabolic pathway demonstrated by 

 these workers may be confined, for the most part, to those cells which 

 are in process of preparing for cell division. There are several observa- 

 tions which tend to support this view. The studies of Mazia and Prescott 

 (1954) indicate that uptake of P-^- in the ameba decreases markedly at 

 the time of cell division, suggesting a reduced capacity to esterify in- 

 organic phosphate at this stage of the mitotic cycle. As already pointed 

 out, the premitotic period, in plant cells at least, is associated with an 

 increase in oxygen consumption (Erickson, 1947; Stern and Kirk, 

 1948). The metabolic changes reported by Taylor (1959) to occur 

 during the premeiotic period in lily anthers could well be controlled by 

 a metabolic pathway of the type shown by Allfrey and coworkers to be 

 mediated by DNA. According to these workers, DNA controls the syn- 

 thesis of nuclear ATP which, in turn, controls the incorporation of 

 amino acids into protein and the uptake of purines and pyrimidines into 

 nuclear RNA. 



Another observation by the Allfrey group which may be of functional 

 significance in terms of cell division kinetics is that nuclear synthesis of 



158 / CHAPTER 6 



