280 



lOO- 



80 





60. 



w 



o 40 



o i 



a. 



20 _ 



oLi 



H. E. Davenport 



100 



% 80|. 



O 13 mg fkivoprotein 

 added 



_L 



J_ 



_l_ 



No added flavoprotcin 



02 0-4 



mg. flavoprotcin 



0-6 



"O Sn ff2 



Fcrrcdoxin (mg) 



Fig. 1. (Left) Activity of pea-leaf flavoprotein fraction in restoring the 

 capacity of protein-depleted pea chloroplast fragments to photoreduce 

 NADP in the presence of saturating concentration of ferredoxin. Ex- 

 perimental conditions as for NADP reduction in Table 1 except that 

 each cell contained pea chloroplast fragments extracted six tinnes with 

 water and equivalent to 0- 025 mg chlorophyll. D, Experimental; 

 ■ > corrected for dark oxidation. 



Fig. 2. (Right) Activity of pea ferredoxin in mediating NADP photoreduc- 

 tion by protein-depleted pea chloroplast fragments. D, With no further 

 additions; ■> in the presence of a saturating amount (0- 13 mg) of a pea- 

 leaf flavoprotein fraction. Experimental conditions as Fig. 1. 



metal pea or spinach chloroplasts prepared in isotonic sucrose were pretreated 

 for 5 min. in sucrose solution containing 5 x 10"^ M PMA and then washed 

 twice in sucrose solution. Such treated chloroplasts when compared with others 

 which had undergone a similar series of washes in sucrose alone were found, 

 when supplemented by ferredoxin, to retain unchanged their capacity to reduce 

 metmyoglobin. By contrast their NADP reducing capacity was impaired to a 

 large but variable extent. (Table 2) 



It was reported earlier'^' that ferredoxin-catalyzed reduction of NADP 

 is stimulated by the presence in the reaction mixture of a phosphate-accepting 

 mixture consisting of ADP, Mg++ and orthophosphate. The pattern of this 

 stimulation in a reconstituted system of washed pea chloroplasts supplemented 

 by ferredoxin and chloroplast flavoprotein is shown in Fig. 3. Phosphorylation 

 of ADP was shown to accompany the stimulated reaction rate. 



