ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 



315 



the Feulgen reaction (see Chapter 17). They were not precipitated when their solution 

 in M sodium chloride was diluted to a molarity of 0.15. Thej' were precipitated by tri- 

 chloroacetic acid and gave positive biuret, xanthoproteic, Millon, and Hopkins-Cole 

 reactions. Electrophoresis revealed the presence of three components. 



For further purification, the dialyzed crude nucleoprotein solution (190 cc), con- 

 taining a total of 265.1 mg. of N and 16.1 mg. of P, was brought to pH 4.3 by the 

 addition of 2% acetic acid. The mixture in which a precipitate appeared immediately 

 was chilled for 3 hours and centrifuged. The sediment was washed with ice-cold 0.05 M 

 citrate buffer of pH 4.3, dissolved in borate buffer (pH 8.4), and dialyzed. To this 

 solution an equal volume of saturated ammonium sulfate solution was added and the 

 precipitate removed by centrifugation. The supernatant solution was, after prolonged 

 dialysis, evaporated in the frozen state in a vacuum. The purified nucleoprotein 

 formed a white fiber felt and weighed 0.29 g. It contained N 12.1%, P 3.2% (N:P per 

 cent ratio 3.8), accounting for about 60% of the phosphorus of the crude nucleopro- 

 tein fraction. The absorption spectra in the ultraviolet of both the crude and the 

 purified nucleoprotein fractions are reproduced in Fig. 1. 



h. Extraction with Strong Salt Solution 



This procedure, very widely used as the first step in the isolation of 

 deo.xy pentose nucleic acids (see below, Section 111.2), has also been much 



300 280 



260 



240 220 



Fig. 1. Ultraviolet absorption spectra of deo-xypentose nucleoprotein of avian 

 tubercle bacilli in 0.03 M borate buffer at pH 7.9. Curve I, purified nucleoprotein; 

 Curve II, crude nucleoprotein. (Taken from Chargaff and Saidel.'') 



