ENZYMES ATTACKING NUCLEIC ACIDS 585 



activity increases correspondingly, e.g., during 90 days' autolysis, the 

 deoxyribonuclease activity of a yeast extract increased fifty fold according 

 to the results of a viscosimetric assay procedure. The deoxyribonuclease 

 differs from deoxyribonuclease I of pancreas by its pH optimum which is 

 in the region of pH 6. It is insoluble in water but soluble in dilute salt 

 solution. It requires magnesium ions for its activity. The protein inhibitor 

 which is destroyed by various crystallized proteolytic enzymes is specific 

 for the yeast enzyme and has no activity toward deoxyribonuclease I, and 

 toward deoxyribonucleases of thymus and of neurospora. 



Muggleton and Webb^" found in culture filtrates of a soil actinomyces 

 (strain A) a very heat-labile deoxyribonuclease which hydrolyzed DNA 

 and the cores obtained from digests of DNA with deoxyribonuclease I. 



3. "Unspecific" Phosphodiesterases 

 a. Snake Venom Phosphodiesterases 



The internucleotide bonds of PNA and of all deoxyribo- and ribonucleo- 

 tides which do not contain terminal secondary phosphoryl groups in the 

 3 '-position are hydrolyzed by purified extracts of the venoms of a variety 

 of poisonous snakes, e.g., those of Crotalus, of Bothrops, of the Japanese 

 snake "Habu." Since none of these enzymes has been obtained in pure, 

 crystalline form, it is not possible at present to decide as to whether the 

 phosphodiesterases of various snake venoms are identical or not. Histor- 

 ically, the snake venom phosphatases, whose action on nucleic acids was 

 discovered in 1919 by Delezenne and Morel, '^^ are of interest because 

 Akamatsu's concept'^- (1931) of the existence of specific enzymes for the 

 cleavage of phosphomonoesters and of phosphodiesters originated from 

 observations with this group of enzymes. Crude snake venoms with few 

 exceptions contain mixtures of phosphodiesterases and phosphomono- 

 esterases. Hurst and Butler^'^^ succeeded, however, in separating both 

 types of phosphatases chromatographically; Sinsheimcr and Koerner'^^ 

 described a procedure involving alcohol fractionation for the preparation 

 of phosphodiesterase containing only negligible quantities of phospho- 

 monoesterases. 



Specificity. Snake venom phosphodiesterase hydrolyzes not only oligo- 

 nucleotides of the structures defined, but also diphenyl phosphate and 

 6zs-p-nitrophenyl phosphate to the corresponding monoesters and phenols 

 without the formation of inorganic phosphate. It can be assayed by phenol 



131 C. Delezenne and H. Morel, Compt. rend. 168, 241 (1919). 



132 T. Uzawa, J. Biochem. (Japan) 15, 19 (1932). 



133 R. O. Hurst and G. C. Butler, J. Biol. Chem. 193, 91 (1951). 



"" R. L. Sinsheimer and T. J. Koerner, J. Biol. Chem. 198, 293 (1952). 



