Effect of dilution on thermal neutron induced inactivation of deoxyribonuclease I

The activity of irradiated DNase I powders was found to decrease exponentially with increasing doses of both thermal neutrons and gamma radiation. The D37 of 1.9 x 107 rad obtained for the γ-irradiated dry DNase I was about 500-fold higher than that for the H2O solution (for example, 4.0 x 104 rad for 0.5 mg/ml). Taking the molecular weight for DNase I as 62000, the G-values for inactivation were 0.809 (dry DNase I) and 0.198 (the H2O solution) molecules per 100 eV of radiation energy absorbed. On the other hand, the D37 for the thermal neutron irradiated DNase I powders (6.0 x 1014ncm-2) is not so high compared with those for the H2O solution (3.1 x 1014ncm-2) and the D2O solution (5.3 x 1014n cm-2). The D37s of γ-ray and thermal-neutron-irradiated H2O solutions decreased with increasing dilution, whereas those for thermal-neutron-irradiated D2O solutions initially decreased with decreasing concentration, but ceased to decrease at concentrations less than 0.03 mg/ml. (U.K.)