. Elementary biophysics: selected topics . 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. Bi
. Elementary biophysics: selected topics . 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.
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