498 



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



260 



Wavelength, m^ 



Fig. 3. Adenine (Johnson, unpublished). The absorption spectra illustarted here 

 and in Figs. 4-20 will be found drawn to scale in the pocket on the inside back cover 

 of the volume. 



From such data it is possible to select wavelengths and obtain coefficients 

 for the identification and quantitative estimation of bases, nucleosides, 

 and nucleotides obtained from nucleic acids by any of the methods des- 

 cribed in other chapters. 



1. Bases 



In spite of the fact that ultraviolet absorption data for adenine have 

 been reported in at least thirteen separate papers, no set of data has yet 

 been published which can be considered in any way comprehensive. This 

 is equally true of the other purines found in or derived from nucleic acids. 

 It has therefore seemed necessary to undertake a more thorough examin- 

 ation of them. Spectra for adenine, hypoxanthine, guanine, and xanthine 

 (measured with a calibrated Unicam SP 500 spectrophotometer, using 

 specimens all purified by various methods in this laboratory) are given in 

 Figs. 3 to 6, respectively, and corresponding numerical data in Table I. 



Spectral data for adenine and guanine in dilute acid and in some cases 

 at other pH values have been determined recently by Hotchkiss,^'' Cav- 

 alieri et al.,^^ Vischer and Chargaff,^! Kerr et al.p Tsuboi and Stowell,^^ 



2» R. D. Hotchkiss, J. Biol. Chern. 175, 315 (1948). 



" E. Vischer and E. Chargaff, J. Biol. Chem. 176, 703 (1948;. 



