BIOCHEMICAL PROPERTIES OF THE ISOLATED NUCLEUS 



203 



Fig. 8. Effect of varying sodium potassium ra- 

 tio on glycine-i-C" incorporation by isolated thy- 

 mus nuclei. The specific activity of the nuclear 

 protein after 60 minutes' incubation is plotted 

 against the ratio of sodium to potassium ions in 

 the medium, the total salt concentration being 

 held constant. 



100 80 



60 



AO 



20 



90 



C 80 



0) 



o 

 0^ 



70 



10- 



— I 1 1 1 1 1 1 1 1 — 



Pep cent of total chloride asKCl 



mcreasing / mcreasinq 



NqCI +KC1 concentration 

 = 0.584 M 



Percent of total chloride as MaCl 



I I I I I I I I I 



20 



40 



60 



80 



100 



which were the equivalent of sucrose nuclei in this respect. However, neither 

 glycerol nor ethylene glycol at isotonic concentrations could preserve the synthetic 

 capacity of the nuclei. 



These experiments illustrate another useful role of the isolated thymus nucleus. 

 The presence or absence of function can be used as a test for the suitability of an 

 isolation method. Many of the nuclear isolation procedures which now exist em- 

 ploy hypertonic solutions of sucrose, glycerol or ethylene glycol. These procedures 

 have advantages in many tissues because the density of the medium permits the 

 sedimentation of nuclei, while cells and cytoplasmic debris remain in suspension. 

 The methods of Philpot and Stanier (21) and of Chauveau ct al. (9) are especially 

 satisfying in producing optically homogeneous nuclei in a high state of purity. 

 It is unfortunate that thymus nuclei cannot withstand such isolations and fail to 

 retain their biochemical activity after exposure to the hypertonic media employed. 

 Yet the value of the thymus nucleus in testing these and other methods of nu- 

 clear isolation is considerable, and it should serve as a useful guide to the develop- 

 ment of newer procedures for the preparation of pure and synthetically active 

 free nuclei. 



SUMMARY AND CONCLUSION 



The results which have been described are only the first inklings of the chemi- 

 cal nature and potential synthetic capacities of the nucleus. It is now clear that. 



