52 



D. SHUGAR 



195 



200 



215 



220 



225 



205 210 

 A (nryj) 



Fig. 4. Absorption spectra of the sodium salts of UMP and CMP in aqueous, un- 

 buffered medium at approximately neutral pH ( ) and in 0.2 N H 2 S0 4 ( ) 



[from M. V. Buell and R. E. Hansen, J. Biol. Chem. in press (I960)] and of uracil (U) 

 at pH 2.4 [from A. Rorsch, R. Beukers, J. Ijlstra, and W. Berends, Rec. trav. chim. 77, 

 423 (1958)]. For CMP the extinction coefficients should be twice those indicated. 



tion is drawn to this relatively new field particularly because of its potential 

 importance in the analysis of stable and reversible photoproducts of pyrimi- 

 dine derivatives. 59 



3. DlHYDROPYRIMIDINE DERIVATIVES 



Saturation of the 4 , 5 double bond of pyrimidine derivatives results in a 

 disappearance of the characteristic absorption maxima in the neighborhood 

 of 260-280 mju, 60 a fact also evident from the spectral characteristics of 



68 E. R. Blout and H. Lenormant, Biochim. et Biophys. Acta 17, 325 (1955). 



59 A. M. Moore and C. H. Thomson, Science 122, 594 (1955). 



60 R. D. Batt, J. K. Martin, J. McT. Ploeser, and J. Murray, J. Am. Chem. Soc. 76, 

 3663 (1954). 



