344 



ERWIN CHARGAFF 



290 



250 



220 



Fig. 3. Absorption spectra in the ultraviolet of sodium deoxyribonucleate of calf 

 thymus (T-DNA) and of the sodium salt of the corresponding apurinic acid (APA) 

 in phosphate buffer of pH 7.1. (Taken from Tamm et al.^'"') 



at 238 m,x with an e(P) of 2900."" "i When the extinction coefficient is 

 computed with respect to nucleotide P rather than to total P, the cor- 

 responding e(NP) at the maximum is found at 9800 to 10,400: another 

 example of the hyperchromic effect of degradation mentioned above in 

 Section IV. The specific rotation [a]^ is +50°, the atomic rotation with 

 respect to phosphorus [M]f(P) is +140°. (Compare Section IV. 1.) 



Other physical and chemical properties of apurinic acid and its deriva- 

 tives have been discussed by Tamm and Chargaff .^'^ In contrast to deoxy- 

 pentose nucleates, apurinic acid reduces Fehling's or Benedict's solution 

 on warming and reacts with ammoniacal silver solution. It gives a strong 

 Schiff test with reduced fuchsin at room temperature. It consumes one 

 mole of potassium bisulfite per mole of nonglycosidic sugar phosphate and 

 is stable toward periodic acid. It yields an oxime, a 2,4-dinitrophenyl- 

 hydrazone, and a benzyl mercaptal which is cleaved by alkali. 



Apurinic acid preparations may be obtained from a large variety of 

 different deoxypentose nucleic acids. They have proved convenient inter- 

 mediates in the search for trace pyrimidines in nucleic acids.'"^'*^'"" In 

 addition, two points should be stressed, (a) Apurinic acid, while still a 

 polynucleotide, has an average molecular weight (estimated at 15,000^^^) 

 that is much smaller than that of the nucleic acid from which it is pre- 

 pared, (b) Apurinic acid is, in its composition, characteristic of the particu- 

 lar deoxypentose nucleic acid that served as the starting material. The use 

 of preparations of this type in structural studies will be considered later. 



"« C. Tamm and E. Chargaff, /. Biol. Chem. 203, 689 (1953). 



