DISULFIDE PHOTOREDUCTION 



311 



induction, as illustrated by the effect of acetone (Fig. 3), The induction 

 period is characteristic of a large number of light- activated redox 

 processes in chromatophores, including photooxidation and photore- 

 duction reactions, and is freely reversible; i.e., particles carrying 

 out photo reactions undergo induction periods again when diluted with 



Preincubation 



1.0 - 



0.5 



Light, DPIP-/ 

 Ascorbate/ 



/ 



Dark, DPIP- 

 Ascorbate 



.c- 



5 10 



Time, Minutes 



Fig. 4. Preincubation effect on induction period during disulfide photo- 

 reduction. Chromatophores were preincubated in light and dark with and 

 without an ascorbate-indophcnol system for 10 minutes. The methyl 

 viologen-DTNB acceptor system was then added and the reaction followed 

 spectrophotometrically in light. Atmosphere, helium. 



media of low ionic strength. Finally, the induction period is inversely 

 proportional to ionic strength over a wide range. 



The reversibility of the induction period suggested an "active" 

 process associated with photochemical electron transport in chroma- 

 tophores. Consequently, the effects of preincubation of chromatophores 

 in light and dark under various conditions on subsequent photochemical 

 activity of the particles were examined. Data in Fig. 4 show that in a 



