ENZYMES ATTACKING NUCLEIC ACIDS 583 



deoxyribonuclease I were also found in other animal tissues and in certain 

 malignant tumors. In the pigeon crop glands, the concentration of the 

 inhibitor protein is strongly increased during the hypertrophy of the 

 epithelium occurring in glands of brooding birds; in other animal tissues, 

 however, no definite correlation between inhibitor concentrations and cell 

 growth could be established so far. Cooper, Trautman, and Laskowski 

 demonstrated the presence of inhibition of deoxyribonuclease I in various 

 mammalian tissues.^" Henstell and Freedman"' reported considerable 

 inhibitory influence of extracts from mature white blood cells on pancreas 

 deoxyribonuclease I. The concentration of this inhibiting activity was 

 greatly diminished in white blood cells of leukemia patients"^ provided 

 that immature cells were predominant in the blood. Kurnick ct ai."'* corre- 

 lated changes of the inhibiting activity of the white blood cells with the 

 characteristic appearance of the L. E. cells in the blood and bone marrow 

 of patients with lupus erythematosus."* McCarty demonstrated specific 

 antigenic effects of purified preparations of pancreas deoxyribonuclease."® 

 Bernheimer and Ruffier"^ found that extracts of streptococci contained an 

 inhibitor of pancreas deoxyribonuclease I, the activity of which was de- 

 stroyed by the action of ribonuclease."^ 



pH Optimum. Deoxyribonuclease I has maximal activity between pH 6 

 and pH 7. The precise values of the pH optimum differ somewhat for 

 different kinds of activating bivalent cations. ^°* 



Deoxynbonudease I as a Protein. Owing to the small yields (Kunitz 

 obtained from 10 kg. of pancreas approximately 20 mg. of the enzyme), 

 information regarding the chemical properties of deoxyribonuclease I is 

 much less extensive than the corresponding data available for crystallized 

 ribonuclease. 



The molecular weight of deoxyribonuclease I (based on its diffusion in 

 the Northrop-Anson cell) was found by Kunitz^'' to be approximately 

 60,000. It contains 8 % of tyrosine and 2 % of tryptophan. The ultraviolet 

 absorption of deoxyribonuclease I is a consequence of the presence of these 

 two amino acids in the molecule. 



The pH of minimal electrophoretic mobility is approximately 5. 



1" E. J. Cooper, M. L. Trautmann, and M. Laskowski, Proc. Soc. Exptl. Biol. Med. 



73, 219 (1950). 

 "2 H. H. Henstell and R. L. Freedman, Cancer Research 12, 341 (1952). 

 "3 H. H. Henstell, R. L. Freedman, and B. Ginsburg, Cancer Research 12, 346 (1952). 

 "4 N. B. Kurnick, L. I. Schwartz, S. Pariser, and S. L. Lee, /. Clin. Invest. 52, 193 



(1953). 

 "6 S. L. Lee, S. R. Michael, and L L. Vural, Aju. J. Med. 10, 446 (1951). 

 116 M. McCarty, J. Gen. Physiol. 29, 123 (1946). 

 1" A. W. Bernheimer and N. K. Ruffier, J. Exptl. Med. 93, 399 (1951). 



