30. PHOTOCHEMISTRY OF NUCLEIC ACIDS ()1 



optical absorption from chemical composition 97 ' 98 suggest that for TMV 

 about 50% of the apparent absorption at 253.7 mp. is due to scattered light; 

 but the validity of such a procedure is questionable. 



From the absorption spectrum of TMV corrected for scattering, Reddi 95 

 subtracts the protein absorption to obtain an c(P) for the nucleic acid com- 

 ponent which is approximately equal to the e(P) of the nucleic acid isolated 

 directly from the virus. It is concluded from this that the aromatic rings 

 are not involved in the linkages between protein and nucleic acid in TMV. 

 However, the Rayleigh procedure for correcting for scattering is subject to 

 considerable error in the neighborhood of an absorption band, as well as 

 for particles such as TMV which are of the same order of magnitude as the 

 wavelength of the light, 99 so that the conclusion that the main linkage in 

 TMV is between the ribonucleic acid (RNA) phosphate groups and protein 

 guanidine groups requires independent substantiation; the more so since 

 the protein component of various TMV strains appears to affect appreciably 

 the photochemical behavior of the virus RNA. 



V. Photochemistry of Nucleic Acid Constituents 



A knowledge of the photochemical behavior of nucleic acid derivatives is 

 an obvious prerequisite to any attempts to interpret the effects of radiation 

 on polynucleotide chains. It should also be borne in mind that living cells 

 contain a considerable pool of free nucleotides as well as nucleotide coen- 

 zymes through which radiation effects may likewise be manifested. For 

 instance, a reasonable correspondence has been established between the 

 destruction of adenosine triphosphate (ATP) and the mobility and fertiliz- 

 ing capacity of frog spermatozoa under the influence of irradiation. 100 In 

 view of the demonstrated involvement of uridinediphosphate glucoside 

 (UDPG) in sucrose synthesis in plants, it is perhaps more than a coincidence 

 that the rate of photolysis of UDPG is comparable to the rate at which 

 inhibition of sucrose synthesis in plants occurs under the influence of irra- 

 diation. 101 Another example of considerable significance is the observation 

 of Haas and Doudney 102 on mutation enhancement by ultraviolet irradiation 



97 A. Butenandt, M. Friedrich-Freksa, S. Hart wig, and G. Scheide, Z. physiol. 

 Chem. 274, 276 (1942). 



98 G. Oster and A. I). McLaren, J. Gen. Physiol. 33, 215 (1950). 



99 K. A. Stacey, "Light Scattering in Physical Chemistry." Butterworths, London, 

 1956. 



100 1). Kanazir and M. Errera, Biochim. el Biophys. Ada 16, 198 (1955). 



101 L. P. Zill, Federation Pro,-. 16, 276 (1957); L. P. Zill and N. E. Tolbert, Arch. Bio- 

 chem. Biophys. 76, 196 (1958). 



102 F. L. Haas and C. O. Doudney, Proc. Natl. Acad. Sci. U. S. 43, 871 (1957); 44, 390 

 (1958). 



