PURINES AND PYRIMIDINES 9 



mercury complexes which then were made visible by their con- 

 version to mercuric sulfide. The papers thus developed served 

 as guide strips for the removal of the corresponding zones from 

 untreated chromatograms that were then extracted and analyzed 

 in the ultraviolet spectrophotometer. The development of the 

 separated bases as mercury derivatives has, however, now become 

 unnecessary, except for the preservation of permanent records, 

 since there has for some time been available commercially an 

 ultraviolet lamp emitting short-wave ultraviolet ("Mineralight", 

 Ultraviolet Products Corp., Los Angeles, California). With the 

 help of this lamp it is now easy to demonstrate directly the 

 position of the separated purines and pyrimidines (and also of 

 nucleosides and nucleotides^^) which appear as dark absorption 

 shadows on the background of the fluorescing filter paper and 

 can be cut apart accordingly. (We are greatly indebted to Dr. C. 

 E. Carter, Oak Ridge National Laboratory, who drew our at- 

 tention to this instrument*.) 



The extracts of the separated compounds are then studied in 

 the ultraviolet spectrophotometer. The measurement of complete 

 absorption spectra permits the determination of the purity of the 

 solutions and at the same time the quantitative estimation of their 

 contents. The details of the procedures employed have been 

 pubhshed^*. In this manner, adenine, guanine, uracil, cytosine, 

 and thymine (and also hypoxanthine, xanthine, and 5-methyl- 

 cytosine) can be determined quantitatively in amounts of 2-40 

 jLig. The precision of the method is ±: 4% for the purines and 

 even better for the pyrimidines, if the averages of a large series 

 of determinations are considered. In individual estimations the 

 accuracy is about d= 6%. 



Procedures very similar in principle served in our laboratory 

 for the separation and estimation of the ribonucleosides uridine 

 and cytidine and for the separation of deoxyribothymidine from 

 thymine. Methods for the separation and quantitative determina- 

 tion of the ribonucleotides in an aqueous ammonium isobuty- 

 rate — isobutyric acid system have likewise been developed^^- 27. 

 * A similar arrangement was recently described^s. 



References p. 23 



