584 G. SCHMIDT 



h. Other Deoxyribonucleases 



Recent observations from several laboratories demonstrated the exist- 

 ence of several different enzymes catalyzing the cleavage of the internu- 

 cleotide bonds of DNA."^ 



Maver and Greco®^-^® and Brown, Jacobs, and Laskowski"^ found that 

 the considerable deoxyribonuclease activity of thymus glands is largely 

 due to the presence of an enzyme which can be differentiated from deoxy- 

 ribonuclease I. Laskowski and his collaborators^^^-^-^ as well as Webb'-'^^^ 

 succeeded in purifying the extractable fraction of thymus deoxyribonu- 

 clease several hundred fold. The enzyme was inhibited by 0.025 M mag- 

 nesium sulfate, but it was not affected by 0.005 M magnesium sulfate. Its 

 activity was not influenced by the specific protein inhibitor of deoxyribo- 

 nuclease I. Its pH optimum was at pH 5. 



Thymus deoxyribonuclease II hydrolyzes DNA without the formation of 

 undialyzable cores. 



The association of the tissue deoxyribonucleases with particulate frac- 

 tions^^*'^-^ is discussed in Section X of this Chapter. 



Deoxyribonucleases of Plants. The occurrence of deoxyribonucleases in 

 plants has been reported,^--* '^-^ but very little detailed information concern- 

 ing the properties of these enzymes is as yet available. The high concen- 

 trations of deoxyribonuclease activity in various germinating seeds^"^'^'* 

 are of particular interest. 



Deoxyribonucleases of Microorganisms. Various microorganisms^"^ 'i-^-^^" 

 contain highly active deoxyribonucleases. Only a few of these enzymes 

 have so far been studied in some detail. Zamenhof and Chargaff^''^ obtained 

 from extracts of bakers' yeast a complex of a deoxyribonuclease with a 

 specific inhibitor protein by precipitation in 0.6 saturated ammonium 

 sulfate solution. On prolonged autolysis at low temperature, the inhibitor 

 protein is destroyed by proteolytic enzymes, and the deoxyribonuclease 



118 G. Herbert, K. Lang, and A. Corbet, Biochem. Z. 320, 418 (1950). 



n9 K. D. Brown, G. Jacobs, and M. Laskowski, J. Biol. Chem. 194, 445 (1952). 



120 M. Laskowski, E. A. Steberl, R. Akka, and P. Watson, Biochirn. et Biophys. Ada 

 (1954), in press. 



121 M. Privat de Garilhe and M. Laskowski, Biochirn. et Biophys Acta (1954), in press. 

 1" M. Webb, Exptl. Cell Research 5, 27 (1953). 



123 M. Webb, Exptl. Cell Research 5, 16 (1953). 



124 J. P. Greenstein, Federation Proc. 1, 113 (1942). 



125 G. Brawermann and E. Chargaff, J. Biol. Chein. 210, 445 (1954). 



126 H. Plenge, Z. physiol. Chem. 39, 190 (1903). 



127 M. McCarty and O. T. Avery, J. Exptl. Med. 83, 97 (1946). 



128 S. S. Cohen, J. Biol. Chem. 168, 511 (1947). 



129 W. S. T. Tillett, S. Sherry, and L. R. Christensen, Proc. Soc. Exptl. Biol. Med. 68, 

 184 (1948). 



130 W. C. Schneider and C. H. Hogeboom, J. Biol. Chem. 198, 155 (1952). 



