STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



79 



oxidative phosphorylation of mitochondria, do not mhibit phosphorylation in 

 the nucleus. Osawa et al. (1957) have suggested that phosphorylation in the 

 nucleus is oxidative and mvolves a cytochrome, as yet undetected. Since one 

 must postulate an as yet undetected cytochrome, it seems equally plausible 

 to consider the possible existence of other as yet undetected oxidation- 

 reduction systems involved in oxidative phosphorylation, and one may 

 wonder if the glutathione-ascorbate systems are not of interest m this 

 regard. 



Protein synthesis m isolated nuclei has been studied by Allfrey et al. 

 (1957a,b). Thymocyte nuclei, isolated in sucrose, have been the major 

 objects of study; these have been incubated with radioactive amino acids in 

 the presence of 0.07 M Na+ and the incorporation of the amino acids into 

 isolated nuclear proteins were followed, as in Fig. 11. L-amino acids are 



300 



O . 30 60 90 120 



Time (min) 



Fig. 11. The time course of incorporation of isotopic amino acids into the isolated 

 thymus nuclei (Allfrey et al., 1957a and b). 



incorporated specifically in a mechanism which does not involve exchange. 

 Under the best conditions of in vitro synthesis obtained, it has been 

 estimated that each nucleus synthesizes 22 molecules of protein of average 

 molecular weight 50,000 per second; this is a very small amount of 

 synthesis. 



The synthesis is inhibited by cyanide, azide, dinitrophenol, dicumarol, etc. 

 However, methylene blue, which inhibits oxidative phosphorylation in 

 mitochondria, and fluoride, which uihibits glycolysis, are relatively without 

 effect. Chloroamphenicol and ethionine, which block protein synthesis very 

 considerably in intact cells, had httle effect on amino acid mcorporation in 

 nuclei. Small amounts of cortisone reduced uptake of C^^-alanine by more 

 VOL. I — 7 



