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A. W. FKENKEL 



photochemical oxidant (OH) will preferentially react back directly 

 with the photochemical reductant (H) (5), this reaction not being 

 accompanied by phosphorylation. However, once electron transport 



Fig. 1. The effect of light and darkness on the levels of orthophosphate and of 

 labile phosphate (hydrolyzed in 7 minutes by A' HCl at 100°C.) in the presence of 

 crude preparations with and without added ADP. (O) orthophosphate taken up, 

 (m) labile phosphate formed. Preparations in 0.2 M glycylglycine (potassium 

 salt) containing 13.4 mg. dry weight protein per vessel with the following addi- 

 tions: 35 mM MgClo, 30 mM KF, 20 fxM orthophosphate, 10.3 fxM ADP, 1.5 mM 

 DPN; final volume per vessel 3.0 ml, pH of reaction mixture 7.4. Temperature 

 25°C. Light intensity 1200 foot-candles (incandescent lamps). Gas phase 

 helium. 



has been initiated through the carrier chain which is associated with a 

 phosphorylating system, this pathway can be maintained by alter- 

 nate oxidation and reduction of the carrier system by (OH) and (H). 

 In addition, there is good evidence that the reducing agent plays a 

 role in protecting the system from inacti^'ation, most likely by photo- 

 oxidation (1,3b), occurring even at rather low partial pressures of 



