330 ELECTRON TRANSPORT 



Light-Induced Oxygen Uptake. 



Lyophilized preparations of the most highly pigmented fraction 

 separated from cell-free extracts were tested for oxygen uptake. 

 Oxygen uptake was not observed in the dark; however, light-induced 

 activity was observed with or without the addition of exogenous sub- 

 strates. Addition of succinate or ascorbate stimulated oxygen uptake, 

 the latter substrate being the most effective. 



Oxygen uptake by suspensions of the lyophilized preparation was also 

 measured after isooctane extraction. The activities of various prepara- 

 tions, i.e., (a) the original lyophilized preparation, (b) isooctane- 

 extracted material, and (c) extracted material with the addition of the 

 isooctane extract, were measured and compared in the presence of 

 ascorbate. As shown in Table 4, the highest rates were observed in the 

 isooctane- extracted preparation whereas the unextracted preparation 

 had the lowest rate of oxygen uptake. The isooctane extract contained 

 material which had an absorption maximum at 270 m/i which dis- 

 appeared upon reduction with sodium borohydride. PCMB (10-4 M) did 

 not affect the rate of oxygen uptake by the unextracted lyophilized 

 preparation whereas treatment with digitonin doubled the rate, 



TABLE 4. 



Effect of isooctane extract upon the light-induced oxidation of ascorbic acid 



Extracted, then 

 Exp. Extracted Extract back Original 



Added 



Rate of Oxygen #1 .083 .077 .058 



Uptake, 

 //moles/min./ 

 O.D. 800 mn #2 .076 .040 .013 



The stimulation by light of oxygen uptake by intact cells of /?. 

 vannielii and Rhodopseudomouas paliistris can be readily observed 

 in the presence of ascorbate. It is clear, however, that the effect is 

 considerably increased by using cell-free extracts. Since extraction 

 with isooctane or digitonin treatment also increases the rate of oxygen 

 uptake, it may well be that breakage of the cells disrupts in some 

 manner the normal electron transport chain that exists in vivo. The 

 increase in light-induced oxygen uptake by isooctane extraction also 

 indicates that quinone(s) are an integral part of the electron transport 

 chain. The lack of inhibition by PCMB indicates also that PPNR or a 

 PPNR-like factor is not involved in photooxidase activity. From these 

 data, and the results of recent experiments, it appears that light- 



