140 METABOLISM AND PHYSIOLOGY 



TABLE 3 



Activation of antiiuycin-resistant cyclic photophosphorylation 

 by DP IP and "redox buffers"* 



Experiment Temperature 



30°C. 



20°C. 



Ascorbate (0.2//mole) + DPIP 

 (0.2 //mole) (0.2 //mole) 



Ascorbate + DPIP + antimycin A 5.0 



Ascorbate + DPIP + NAD (1 //mole) 7.5 



Ascrobate + DPIP + NAD 

 + antimycin A 



5.1 



* After Bose and Gest (47). In experiment I, the R. riibnDn particles contained 

 0.11 mg bacteriochlorophyll; in experiment II, 0.20 mg. The reaction mix- 

 tures contained in a final volume of 3 ml: particles; Tris-HCl pH 8.0, 100 

 //moles; ADP, 0.5 //mole; K2HPO4, 10.2 //moles; MgS04, 5 //moles; hexo- 

 kinasc, 1 mg; glucose, 30 //moles. Gas phase, H2; incubation time, SOminutes 

 in red light. 



As an alternative to "noncyclic electron flow," studies by a number 

 of investigators, notably Chance and his colleagues (50,51), have pro- 

 vided the basisfor a completely different, but at least equally plausible, 

 mechanism for light- stimulated electron transfer between added 

 donors and acceptors. These researches, with mammalian mitochon- 

 dria, indicate that electron flow against an apparent thermochemical 

 gradient can be driven by energy-generating systems. The reaction 

 which has been studied in most detail is the reduction of NAD by suc- 

 cinate, i.e., 



X "^ or X "^ P 

 succinate + NAD ^fumarate + NADH 



