146 



LIGHT AND LIFE 



220 



380 



260 300 340 



WAVELENGTH ( m/A ) 



Fig. 1. Fluorescence excitation spectra of alpha and beta DPNH. Curve A, fluore- 

 scence excitatif)n spectrum of beta DPNH 1.5 X 10"' M, in water. Fluorescence 

 maximum z= !()2 ni/x. Cur\e B, fluorescence excitation spectrum of alpha DPNH, 

 1.5 X 10-* M. in water. The spectra were studied at ri°C. and corrections arc made 

 for the variation in intensity of the exciting light. 



bonded to the thiocarl^onyl function. That the same kind of inter- 

 action occurs in the DPNH molecule is suggested from the fact that 

 replacement of the amino grouji by a hydroxyl in deamino-DPNH 

 reduces the efficiency of intramolecular excitation energy transfer 

 (20) . Modification of the adenine moiety by reacting DPN with 

 ethylene oxide was carried out by Dr. VVinchnueller of oin- labora- 

 tory. The structure of the reduced compound luuler the conditions 

 for studying excitation energy transfer is given in Fig. 4. While 

 the E.jco/E-n,^ ratio for this compound is the same as that found in 

 DPNH, the modified material shows no transfer of energy from 260 

 ni/x excitation to the (hhydronicotinamidc moiety. 



