231 



C. C. Black and A. San Pietro 



200 



0. ^ 150 



< -I 



E I 



100- 



o 



_i 

 o 



2 



.05 I .15 



ml of PHOSPHODOXIN 



10 15 



MINUTES 



20 



Fig. 3. (Left) Effect of concentrations of spinach phosphodoxin 

 on photophosphorylation with spinach chloroplast fragments. 

 Fig. 4. (Right) Time course and effect of anaerobic conditions 

 on photophosphorylation with spinach chloroplast fragments plus 

 spinach phosphodoxin. 



inhibition was obtained with the following compounds at t he indicated concen- 

 trations: atebrin, 10'^ M; antimycin A, 4 x 10"^ M; Cd , 10"^ M; and 

 NH4"'", 6 X 10'"* M. Arsenite at concentrations as high as 10' ^ M did not 

 affect photophosphorylation with spinach phosphodoxin. 



Since phosphodoxin is a naturally occurring catalyst, it was of interest 

 to study photophosphorylation in the presence of other known catalysts. 

 Total photophosphorylation in the presence of NADP and PPNR plus increas- 

 ing amounts of spinach phosphodoxin did not change from that observed 

 with only NADP and PPNR. In the presence of ferricyanide, a definite in- 

 hibition of ATP production was observed. A distinct stimulation of PMS- 

 catalyzed photophosphorylation was observed, varying between 2- and 4-fold 

 at low levels of phosphodoxin. 



Spinach phosphodoxin is active with chloroplasts from higher plants and 

 chromatophores from photos ynthetic bacteria. Conversely, phosphodoxin 

 from photos ynthetic bacteria is active with spinach chloroplast fragments. 

 This crossing of activity irrespective of the photos ynthetic organisms from 

 which the phosphodoxin was isolated is illustrated in Table 1 and in Fig. 7. 

 Further demonstrations of this crossing of activity are given in references 

 21 and 22. 



