432 



R. M. S. SMELLIE 



^^^'y^^^UR\D\UE PHOSPHATES 



MfO- 



-ACID-SOL UMP 



'ACID-SOL UMP 

 (HCL ELUATE) 



50- 



40 



30 



20- 

 10 

 



NUC PNA 

 URIDYL IC 



ACID 



y^ZZ4 8 HOURS 6 



Fig. 7. Specific activities of uridine phosphates from the acid-soluble fraction and 

 from the nPNA of rat liver at different times after the administration of orotic 

 acid-6-C^*. "Acid-soluble UMP" is the free uridine-5'-monophosphate of the acid 

 extract. "Acid-soluble UMP (HCl eluate)" represents the activity of the uridine de- 

 rivatives obtained by hydrolysis of the mixture of uridine compounds which are 

 eluted from the ion-exchange column with HCl (Hurlbert and Potter^'i). 



out by Smellie et aZ.-'^^i^ These tissues fall into three categories according 

 to their relative rates of DNA turnover: 



1. Kidney in which the renewal of DNA is very slight. 



2. Appendix and bone marrow in which the DNA turnover is very rapid, 

 being greater than that of the cPNA and only slightly lower than that of 

 the nPNA. 



3. Intestinal mucosa, spleen, and thymus where the DNA is replaced 

 at a rate intermediate between that of kidney and bone marrow and lower 

 than either nPNA or cPNA. 



In all the tissues examined, the activities of the nPNA's rose very sharply, 

 reaching maxima earlier and higher than the corresponding DNA's and 

 cPNA's. The turnover of appendix and bone marrow cPNA was also 

 rapid, being only slightly lower than that of the DNA's; in the other tis- 

 sues, however, cPNA renewal was more moderate. 



Klein and Forssberg-'^ have examined the effects of X-irradiation on 

 the metabolism of the nucleic acids in Ehrlich mouse ascites tumor. A dose 

 of 1250 r. of X-rays completely inhibited mitosis over a period of 16 hr. 

 without producing any increase in cell death rate. In these conditions a 

 linear increase in cell volume occurred with time and the increase in PNA 

 per cell corresponded to the increase in volume. On the other hand, the 

 DNA per cell was raised only slightly. Further studies using glycine-2-C^^ "^^ 



21* R. M. S. Smellie, G. F. Humphrey, E. R. M. Kay, and J. N. Davidson, Biochem. 



J.5S, xxxvii (1954). 

 "6 R. M. S. Smellie, G. F. Humphrey, E. R. M. Kay, and J. N. Davidson, Biochem. 



J. in press 1955. 

 "6 G. Klein and A. Forssberg, Exptl. Cell Research 6, 211 (1954). 

 "' A. Forssberg and G. Klein, Exptl. Cell Research, 7, 480 (1954). 



