246 G. R. WYATT 



method of detecting purines'^ depends on their conversion to silver salts. 

 Purines may also be made visible by staining their mercury complexes with 

 eosin or bromphenol blue, or by their fluorescence after exposure to chlor- 

 ine. ^^ A microbiological method for detecting purines and pyrimidine nucleo- 

 sides on paper chromatograms with the aid of deficient strains of Ophios- 

 toma has been used by Fries et al}'' In general, however, the most convenient 

 techniques are those taking advantage of the absorption of ultraviolet light 

 by the nucleic acid bases. 



When a paper chromatogram is examined under an ultraviolet lamp hav- 

 ing a high emission in the range of maximal nucleic acid absorption, and 

 with visible light efficiently filtered out, spots of nucleic acid components 

 appear as dark regions against the background fluorescence of the filter 

 paper.^^"^^ A low-pressure mercury resonance lamp is suitable, and it is re- 

 ported that 0.2 ng. of adenine spread over a circle 1.5 cm. in diameter can 

 be detected.-'* 



Another procedure of approximately equal sensitivity, which is more laborious 

 but provides a permanent record of each chromatogram, consists in making photo- 

 graphic contact prints in ultraviolet light. ^^^ ^^ A medium- or high-pressure mercury 

 lamp is used, with a filter system which isolates the 253.7-m/i and 265-myii emission 

 lines. 2' The dried paper chromatogram is pinned over a sheet of photographic paper 

 (a contact document or photostat paper is suitable) on a board and exposed to the 

 lamp for an appropriate time (usually less than a minute). In the developed print, 



18 R. M. Reguera and I. Asimov, /. Am. Chem. Soc. 72, 5781 (1950). 



19 H. Michl, Naturwissenschaflen 40, 390 (1953). 



2" N. Fries and U. Bjorkman, Physiol. Plantarum 2, 212 (1949) ; N. Fries and B. Fors- 

 man, ibid. 4, 410 (1951). 



21 E. R. Holiday and E. A. Johnson, Nature, 163, 216 (1949). 



21a E. Chargaff, B. Magasanik, R. Doniger, and E. Vischer, /. Am. Chem. Soc. 71, 

 1513 (1949). 



" C. E. Carter, J. Am. Chem. Soc. 72, 1466 (1950). 



23 T. Wieland and L. Bauer, Angew. Chem. 63, 511 (1951). 



2^ Marshak^'i reports this sensitivity using a General Electric Co. lamp No. G8T5 

 equipped with Corning filter No. 9863. "Mineralight" lamps have been widely 

 used, but are rather less sensitive. The effect has been photographed by J. P. Goel- 

 ler and S. Sherry, Proc. Soc. Exptl. Biol. Med. 74, 381 (1950). 



26 R. Markham and J. D. Smith, Nature 163, 250 (1949). 



26 R. Markham and J. D. Smith, Biochem. J. 45, 294 (1949). 



2' Markham and Smith^" recommend the Mazda MB/V lamp with the glass bulb 

 removed, and a filter system made with two 25-ml. fused silica round-bottomed 

 flasks containing, respectively, a solution of cobalt and nickel sulfates (CoS04- 

 7H2O 10 g. and NiS04 35 g. per 100 ml.) and dry chlorine gas. The writer has found 

 satisfactory a General Electric AH-4 lamp equipped with this filter system. The 

 chlorine gas filter may be replaced by a 1-cm. layer of chlorine dissolved in carbon 

 tetrachloride. 39 The system transmits too much visible light to be satisfactory for 

 making spots visible by fluorescence quenching, but by adding a Corning filter 

 No. 9863 or by viewing the chromatograms through a blue filter, one may use it in 

 this way too. 



