64 



LIGHT ABSORPTION EFFECTS 



o 



Nucleic acid 



CO 



CO 

 OS 



Co 



240 260 280 300 

 Wavelength in mn 



(a) 



240 260 280 300 

 Wavelength in m^u 



(b) 



Fig. 28. Part (a) shows the absorption spectra of equal concentrations of nu- 

 cleic acid and protein. Part (b) shows the action spectrum for inactivating the 

 capacity of Euglena cells to form photosynthetic progeny. Its peaks at 260 and 

 2S0 mfi show that both nucleic acids and proteins are involved in this experi- 

 ment, in which irradiated cells give rise to white, nonphotosynthetic colonies in 

 place of the normal green colonies from unirradiated cells. (After H. Lyman, 

 H. T. Epstein, and J. A. Scruff, Biochem. Biophys. Acta 50, 301, 1961.) 



of single cells are inactivated by exposure to ultraviolet light to the 

 extent that they are actually killed. 



In these instances, we measure the inactivation spectrum from about 

 220 m/A to about 350 m/u. In this region the nucleic acids and proteins 

 are the chief pigments, and one usually learns only whether one or both 

 are implicated in the inactivation. In the case of enzyme inactivation, 

 only a spectrum similar to protein absorption is obtained. In virus in- 

 activation usually a spectrum resembling nucleic acid absorption is 

 found, although there are instances of effectiveness peaks corresponding 

 to both nucleic acid and protein. The absorption spectra for nucleic 

 acids and proteins are shown in Fig. 28, along with an example of an 

 inactivation spectrum. 



It must be carefully noted, however, that the process being studied 

 need not be viability. To emphasize this point, we present the following 

 list of inactivation spectra possible just for simple organisms such as 

 viruses; more complicated organisms would have an even longer list. 

 One can inactivate viruses with respect to (a) their ability to form viable 

 progeny, lb I their ability to kill cells on which they normally grow, 

 (c) their ability to adsorb to cells, (d) their ability to initiate the produc- 

 tion of various metabolic processes, (e) their ability to participate in 

 genetic recombination. 



