NATURE OF SPLEEN-BONE MARROW RADIATION RECOVERY FACTOR 



gave a negative Dische reaction for DNA ; while the supernatant from A 

 was found to contain 345 [xg DNA per ml, or 3-27mg DNA in the whole 

 supernatant. This represents a solubilization of 43 per cent of the total 

 DNA present in the homogenate. The ultraviolet absorption data on these 

 supernatants, are presented in Figure 3. The high specific absorption at 

 260 mij. of the supernatant from the DNA-ase treated homogenate is again 

 noteworthy. 



The differential effect of DNA-ase on a fresh, non-disrupted spleen cell 

 suspension and on a spleen homogenate containing the same number of 

 whole cells, is evident from Figure 4. 



The experimental data support the view that the DNA as present in fresh, 

 intact, non-homogenized spleen cell suspension is not available as substrate 



700 



5 Homogenate from 

 280 mg spleen e-9 — 

 X W^ ce//s/Tr\X incu- 

 bated Witt) DNA-ase. 

 25°Zfor 30 min. 

 _J \ \ !_ 



ttomoffenate from 

 280 mg spteen 7-9 _ 

 x10^ cetts/-mX I'ncu- 

 6a ted — no ens/me 



300 3W 380 



Woyelenqtti Ta^i. 



Figure 3. Liberation of soluble deoxyribonucleic 

 acid from washed spleen homogenate by 

 deoxyribonuclease 



(J-/ absorption after' 

 incubation witti DNA - 

 ase 25 °C for 30 mm. 

 Suspending medium ^ 

 0-n M NaCl~ 



I I 

 -IVostied homogenate' 

 from 280 mg spleen 

 6-9x10^ c<?//j/m,lj 



Spleen cell suspension 

 57Jc70^celis/wX 



2£0 



300 3V0 

 y/a^'elength 



3SD 

 m^ 



Figure 4. Comparative effect of deoxyribonuclease 

 on spleen cell suspension versus spleen homo- 

 genate 



for the enzymatic action of added DNA-ase. It follows, therefore, that if 

 the protective activity of a given preparation of spleen nuclear fraction, or 

 of a thoroughly homogenized and washed spleen homogenate can be 

 inactivated by short-term incubation with DNA-ase, the active protective 

 principle cannot be a result of the presence of intact, living cells, per se. 

 The protective effect of such preparations would be referable to an infra- 

 cellular Ijiologically active substance or complex. 



THE RECOVERY FACTOR IN RAT BONE MARROW 



The recent finding^ ^ of post-protection of X-irradiated rats afforded by the 

 intravenous injection of homologous rat bone marrow suspension, has now 

 prompted some experiments designed to investigate the properties of the 

 recovery factor in marrow. The pertinent experimental results are summar- 

 ized in Table I. Rat bone marrow homogenates, prepared in sucrose-salt- 

 ATP medium^, containing dextrose (Imgperml) afford definite protection 



144 



