OSWALD T. AVERY, COLIN M. MACLEOD, AND MACLYN MCCARTY 



149 



no significant reduction in viscosity after 22 hours. On the other hand, heating 

 rabbit serum at 60°C. merely reduced the rate of depolymerase action, and 

 after 24 hours the viscosity was brought to the same level as with the unheated 

 serum. Heating at 65°C, however, completely destoyed the rabbit serum 

 depolymerase. 



Thus, in the case of dog and rabbit sera there is a striking parallelism between 

 the temperature of inactivation of the depolymerase and that of the enzyme 

 which destroys the activity of the transforming principle. The fact that this 

 difference in temperature of inactivation is not merely a general property of all 

 enzymes in the sera is evident from experiments on the heat inactivation of 



Dif ferenticd Heat Inactivation 



of Desoxypibonucleodepolymepaee 



of Dog and Rabhit Senum 



Rcbbit serum 

 fc Heated 65° for 30' 



"--•,. Heated 60° for 30' 



10 15 



Time 



Chart 1 



tributyrin esterase in the same samples of serum. In the latter instance, the 

 results are the reverse of those observed with depolymerase since the esterase 

 of rabbit serum is almost completely inactivated at 60°C. while that in dog 

 serum is only slightly affected by exposure to this temperature. 



Of a number of substances tested for their capacity to inhibit the action 

 of the enzyme known to destroy the transforming principle, only sodium fluoride 

 has been found to have a significant inhibitory effect. Regardless of whether 

 this enzyme is derived from pneumococcal cells, dog intestinal mucosa, pan- 

 creatin, or normal sera its activity is inhibited by fluoride. Similarly it has 

 been found that fluoride in the same concentration also inhibits the enzymatic 

 depolymerization of desoxyribonucleic acid. 



The fact that transforming activity is destroyed only by those preparations 

 containing depolymerase for desoxyribonucleic acid and the further fact that 



199 



