PHOTO PHOSPHORYLATION IN R. RUBRUM 219 



is, however, inhibited about 38 per cent. This result is in agreement 

 with the commonly observed bypass of antimycin inhibition by PMS 

 (6). When succinate and PMS are added together one observes again 

 an appreciable inhibition in the presence of antimycin which is by- 

 passed in the presence of UQ2 (compare vessels 3 and 6, Table 1), 

 Thus it would appear that UQ2 by affecting the redox balance of the 

 system even in the presence of antimycin can stimulate or inhibit LIP, 

 This concept is further borne out by a comparison of vessels 2 and 5 

 incubated in the presence of antimycin. Here again one could reason 

 that UQ2 has affected the redox balance of the system being acted on 

 by the light- reduced PMS, in the pathway bypassing antimycin, so 

 that stimulation of LIP is obtained. If one now compares vessels 5 and 

 6 incubated in the presence of antimycin, one must conclude that suc- 

 cinate has affected the redox balance towards over- reduction so that 

 inhibition of LIP occurs. 



Similar results to the foregoing can be obtained from experiments 

 using the ascorbate-DPIP couple which has been used in studies on 

 photooxidation and photoreduction in chromatophore particles (3,5,8). 

 Although the LIP of DPA particles is completely inhibited when high 

 concentrations of ascorbate (4 mM) are used, it is maintained when the 

 concentration is low (0,02 mM), as shown in Table 2. Addition of UQ2 

 or DPIP leads to complete inhibition of phosphorylation, again pre- 

 sumably due to alteration in the redox balance of the system. Addition 

 of UQ2 to the ascorbate-DPIP couple leads again to the establishment 

 of a new redox balance which is favorable for increased LIP, Similarly, 

 addition of DPIP to the ascorbate- UQ2 couple leads to the same effect. 

 In the presence of antimycin the stimulating effect of ascorbate alone 

 is completely abolished. In this sense the DPA particles behave dif- 

 ferently from normal particles where in some cases ascorbate- 

 induced LIP appears to bypass antimycin inhibition (7,8), Upon the 



TABLE 2 

 The Effect of Ascorbate, DPIP and UQ2 on LIP in DPA Particles 



Vessel No. Additions No Antimycin With Antimycin 



Conditions same as for Table 1. Figures represent micromolesof phosphate 

 taken up in 1 hour, using 0.6 mg of chromatophore particle protein. The addi- 

 tions, where indicated, consisted of 0,5 //moles of ascorbate, 0.2 //moles of 

 DPIP and 0.08 //moles of UQ2. 



