310 



ELECTRON TRANSPORT 



such changes precede certain electron transport processes in chroma- 

 tophores. Data in Fig, 2 illustrate a typical d.ss2Ly of R. nib rum 

 chromatophores for photo reduction with the aromatic disulfide 5,5- 

 dithiobis-2-nitrobenzoic acid (DTNB) as a thiol-trapping system. The 

 assays were performed using media of two different ionic strengths. 

 Both preparations carry out the light- activated photo reduction at iden- 

 tical rates, under anaerobic conditions, when the ascorbate-indophenol 

 system is used as the electron donor and methyl viologen as catalyst. 

 However, preparations in media of low ionic strength invariably dis- 

 play induction periods in photochemical activity, which is eliminated 

 by salts. Induction is freely reversible and demonstrable with a large 

 variety of di- and monovalent anions and cations; it is an effect of 

 ionic strength on the particles. That elimination of the induction 

 period is not solely the result of a general solute or osmotic process 

 is indicated, because neither sucrose, urea, nor alcohols at relatively 

 high concentration eliminate induction. In fact, nonionic solutes extend 



Tetrazolium Photoreduction 



0.5 



0.4 - 



E 



o0.3 



O0.2 



Na-P04 /i= 1.2 y 



/7 = 1.2 + 

 O.IM Acetone^ 



^ 





/i=^o^§:r^' 



4 6 8 10 



Time, Minutes 



12 14 



Fig, 3, The effect of acetone on photoreduction of tetrazolium blue by R. 

 r^fin/m chromatophores in media of high ionic strength, Ascorbate-indophenol 

 system is the electron donor. 



