288 



ELECTRON TRANSPORT 



20 



30 40 50 60 



TIME (MINUTES) 



70 



80 



Fig. 8. Effectof light intensity on NAD (DPN) reduction by R. mbntm chroma- 

 tophores. Reduction of NAD was followed by measuring the absorbancy increase 

 at 340 m^. Reactions were carried out at 20° C in vacuum in Thunberg-type 

 cuvette (1-cm. optical path). The standard components of the reaction mixture 

 were as follows: 0.1 M Tris containing 10% sucrose (Tris-sucrose buffer) of 

 pH 8.0, 1.00 ml.; 0.1 M MgCl2, 0.20 ml,; 5.3 x 10-4 m NAD, 0.20 ml.; R. nibriim 

 chromatophores (S) (A 339 m/i/"^^'» approx. 50 ), 0.20 ml. The total volume of 

 cuvette was adjusted to 3.00 ml. with water, and in the side chamber was 0.1 M 

 succinate (pH 8), 0.20 ml. 



succinate/fumerate in darkness, so that when the E^ value of the oxidant 

 is -0.04 V or more negative, electrons do not flow from NADH to fuma- 

 rate. If the E^ value is more positive, it may exceed the capacity of the 

 regulatory mechanism, possibly for phosphorylation. 



Using cell-free extracts from Rhodopseudomonas palustris , Katoh 

 (58) has found that oxygen uptake with succinate in darkness and in 

 light was remarkably inhibited by ADP (half inhibition at 1.25 x 10"^ 

 M). In contrast, with the use of R. nibnim it was recently found that 

 the light- stimulated oxidation of cytochrome C9 by chromatophores 

 was markedly accelerated by the addition of ADP, and co a lesser 

 extent by the addition of Pi (Fig. 10) (Horio and Yamashita, un- 

 published). The addition of both ADP and Pi further accelerated the 

 oxidation, which was not influenced by antimycin A. 



Duysens (59) and Goedheer (60) have reported that bacteriochloro- 

 phyll is oxidatively bleached in light. Using ferri-ferrocyanide, the 



