524 



11.000 

 10,000 



G. H. BEAVEN, E. R. HOLIDAY, AND E. A. JOHNSON 



Fig. 24. Variation of 6(P) of calf thymus DNA with pH. 



(1) Calculated for a mixture of nucleosides containing adenosine, guanosine, cyti- 

 dine, and thymidine in the molar proportions 4:3:3.4. Below pH 2 values for adenine 

 and guanine are employed. 



(2) Titration of calf thymus DNA in absence of salt (Blout and Asadourian''^). 



(3) Titration in 1 M NaCl solution (Frick^^). 



(4) Titration in absence of added salts. 

 (5a) in IQ-^ M MgSOi . 



(5b) In 3.4 X IQ-^ M MgSOi . 



(5c) In 0.1 M NaCl. 



(5d) In M NaCl (Lawley^s). 



is to decrease the pH value at which the increase in e(P) starts to occur 

 (see below). These observations indicate that there are two independent 

 processes, ionization on the one hand and a change of e(P) on the other. 

 On the alkaline side the process responsible for the changes in ^(P) and 

 ionization is concurrent with change in pH, whereas on the acid side, at 

 any rate in the absence of salts, they are independent. 



