AVERY, MACLEOD, MCCARTY 



tested. The alkaline phosphatase activ- 

 ity of these preparations was deter- 

 mined by their action on yS-glycero- 

 phosphate and phenyl phosphate, and 

 the esterase activity by their capacity 

 to split tributyrin. Since the highly 

 purified transforming material isolated 

 from pneumococcal extracts was 

 found to contain desoxyribonucleic 

 acid, these same enzymes were tested 

 for depolymerase activity on known 

 samples of desoxyribonucleic acid iso- 

 lated by Mirsky ^ from fish sperm and 

 mammalian tissues. The results are 

 summarized in Table II in which the 

 phosphatase, esterase, and nucleode- 

 polymerase activity of these enzymes 



183 



is compared with their capacity to 

 destroy the transforming principle. 

 Analysis of these results shows that 

 irrespective of the presence of phos- 

 phatase or esterase only those prepara- 

 tions shown to contain an enzyme 

 capable of depolymerizing authentic 

 samples of desoxyribonucleic acid 

 were found to inactivate the trans- 

 forming principle. 



Greenstein and Jenrette (18) have 

 shown that tissue extracts, as well as 

 the milk and serum of several mam- 

 malian species, contain an enzyme sys- 

 tem which causes depolymerization of 

 desoxv^ibonucleic acid. To this en- 

 zyme system Greenstein has later 



Table II 



The hiactivation of Trajisformiyig Principle by Crude Enzy?fie Freparations 



given the name desoxyribonucleode- 

 polymerase (19). These investigators 

 determined depolymerase activity by 

 following the reduction in viscosity of 

 solutions of sodium desoxyribonu- 

 cleate. The nucleate and enzyme were 

 mixed in the viscosimeter and viscosity 

 measurements made at intervals during 

 incubation at 30°C. In the present 

 study this method was used in the 

 measurement of depolymerase activity 

 except that incubation was carried out 



3 The authors express their thanks to Dr. 

 A. E. INlirsky of the Hospital of The Rocke- 

 feller Institute for these preparations of de- 

 soxyribonucleic acid. 



at 37°C. and, in addition to the reduc- 

 tion of viscosity, the action of the en- 

 zyme was further tested by the pro- 

 gressive decrease in acid precipitability 

 of the nucleate during enzymatic 

 breakdown. 



The effect of fresh normal dog and 

 rabbit serum on the activity of the 

 transforming substance is shown in the 

 following experiment. 



Sera obtained from a normal dog and 

 normal rabbit were diluted with an equal 

 volume of physiological saline. The di- 

 luted serum was divided into three equal 

 portions. One part was heated at 65 °C. 

 for 30 minutes, another at 60 °C. for 30 



