92 D. SHUGAR 



An important consideration is the extent to which the energy absorbed 

 is utilized at the absorption site or transferred to some other cell component 

 where its effect is manifested. Action spectra alone are incapable of resolv- 

 ing this problem and recourse must be had to supplementary experimental 

 data. 



The subject of transference of absorbed energy in excited biological systems has 

 only recently begun to attract attention. A well-known example of such transfer is 

 the dissociation of CO-myoglobin with equal efficiency by light absorbed either in 

 the protein or heme components. 2 ' 3 An illustration of energy transfer from a nucleo- 

 tide coenzyme (DPN) to a protein to which it is bound is provided by triosephosphate 

 dehydrogenase, where light absorbed at the 340 nrux band of enzyme-bound DPNH re- 

 sults in an increase of enzymic activity, presumably by reduction of enzyme — S — S — ■ 

 groups 134 ; an analogous phenomenon in vivo 1 ** has been interpreted on the basis of 

 this mechanism 134 and attention has been drawn to its possible significance in photo- 

 reactivation. 94 ' 181 



Due to the complexity of biological systems, synthetic models have been used to 

 obtain quantitative data. Broser and Lautsch 189 coupled poly-DL- (phenylalanine- 

 glutamic acid) with carbonyl-mesohemin-IX and irradiated the complex at a wave- 

 length corresponding to the phenylalanine absorption band. The resulting dissocia- 

 tion of the CO from the hemin group with a quantum yield of unity was regarded as 

 evidence of highly efficient energy transfer along a polypeptide chain due to overlap- 

 ping amplitude functions of adjacent groups in a helix; but resonance transfer has 

 been suggested as an equally likely interpretation. 



An interesting study has been made of electronic energy transfer by proteins and 

 nucleic acids by preparing dye conjugates of each and measuring the efficiency with 

 which light absorbed by protein or nucleic acid excites dye fluorescence. 190 No such 

 energy transfer by either RNA or DNA could be detected and this was ascribed to 

 the assumed nonfluorescent nature of nucleic acid derivatives in solution. The evi- 

 dence on this latter point is, however, conflicting 39 and requires clarification, particu- 

 larly in view of its importance in resonance transfer of energy, i.e., the transfer of 

 energy by electrodynamical interaction from an excited oscillator to an oscillator in 

 resonance with it and so close to it that their separation is small by comparison with 

 the wavelength of the vibrating electromagnetic field emitted by the former. An ex- 

 cellent presentation of this subject has been given by Karreman and Steele 191 (cf. 

 Biicher 192 ). 



FVom a study of the fluorescence efficiency of TMV and its protein moiety alone, 190 

 it was concluded that energy transfer from protein to nucleic acid is nonexistent but 

 that up to 25% transfer from nucleic acid to protein may exist. However, such is not 

 necessarily the case at short wavelengths (Section IX). Indirect evidence for low 

 energy transfer efficiency from nucleic acid to protein is the well-known fact that 

 virus infectivity may be destroyed by irradiation without appreciably affecting anti- 

 genic properties. 



188 G. Calcutt, Nature 166, 443 (1950). 



189 W. Broser and W. Lautsch, Z. Nalurforsch. lib, 453 (1956). 



190 V. G. Shore and A. B. Pardee, Arch. Biochem. Biophys. 60, 100 (1956); 62, 355 

 (1956). 



191 G. Karreman and R. H. Steele, Biochim. et Biophys. Acta 25, 280 (1957). 



192 T. Biicher, Advances in Enzymol. 14, 1 (1953). 



