576 G. SCHMIDT 



side-containing diesters of phosphoric acid, such as: 



2 cytidine-3'-benzylphosphate 



= cytidylyl-3',5'-cytidylyl-3'-benzylphosphate + benzyl alcohol 



Ribopolynucleotidases of Plants. Bredereck et al.^^-^^ found that aqueous 

 extracts of sweet almonds, lucern seeds, or sprouted peas contain an en- 

 zyme system capable of converting ribonucleate practically completely to 

 the nucleosides and phosphoric acid, at a pH range between 5 and 6. A 

 fractionation of this system has so far not been attempted. 



Bacterial Rihonucleases. Muggleton and Webb^" found in culture filtrates 

 of soil actinomyces (strain A) a very heat-labile ribonuclease, which was 

 capable of hydrolyzing PNA as well as the polynucleotides resistant toward 

 ribonuclease I. The presence of this ribonuclease is responsible for the 

 power of the culture filtrates to render suspensions of heat-killed pneumo- 

 cocci gram-negative. 



2. Deoxyribonucleases 



a. Pancreas Deoxyribonuclease {Deoxy ribonuclease I) 



History. Araki^"^ observed in 1903 that extracts of several tissues such 

 as liver, spleen, and thymus had the power to liquefy gels of deoxyri- 

 bonucleic acid. Abderhalden and Schittenhelm" (1906) as well as de la 

 Blanchardiere^i'^ (1913) found that pancreatic juice of dogs effected this 

 liquefaction without liberation of purine bases or inorganic phosphate. 

 Feulgen72.73 added the important observation that the degradation of 

 deoxyribonucleic acid by pancreas preparations (pancreatin) did not 

 yield mononucleotides, but stopped at the formation of oligonucleotides. 

 Schmidt, Pickels, and Levene^" found in 1938 that the degradation of DNA 

 to oligonucleotides by the pancreas enzyme or by alkali was an essential 

 intermediary step for the enzymic cleavage of DNA to mononucleotides 

 (and subsequently to nucleosides) by the phosphatase of intestinal mucosa. 

 Intestinal phosphatase does not act on highly polymerized DNA, but it 

 hydrolyzes all interlinkages of the mononucleotide groups in the oligo- 

 nucleotide mixture obtained by the action of deoxyribonuclease. Some- 



«8 H. Bredereck and G. Rothe, Ber. 71B, 408 (1938). 



«» H. Bredereck, G. Caro, and F. Richter, Ber. 71B, 2389 (1938). 



70 P. W. Muggleton and M. Webb, Biochim. et Biophys. Acta 9, 343 (1952). 



70a T. Araki, Z. physiol. Chem. 38, 84 (1903). 



" E. Abderhalden and A. Schittenhelm, Z. physiol. Chem. 47, 452 (1906). 



"a P. de la Blanchardiere, Z. physiol. Chem. 87, 291 (1913). 



" R. Feulgen, "Chemie und Physiologie der Nucleinstoffe." Berlin, 1923. 



73 R. Feulgen, Z. physiol. Chem. 237, 261 (1935). 



7" G. Schmidt, E. G. Pickels, and P. A. Levene, /. Biol. Chem. 127, 251 (1939). 



