285 



Giorgio Forti, Maria Luisa Bertole and Bruno Parisi 



and this is indeed observed^^); also, that it should be oxidized in the light by 

 chloroplasts, in the presence of photosynthetic pyridine nucleotide reductase 

 (PPNR) and TPN. This is clearly not the case^^); under no conditions was 

 oxidation of added cytochrome f by chloroplasts or grana observed, in the 

 light or in darkness. Furthermore, the presence of oxidized cyt. £ inhibits 

 the photoreduction of TPN by chloroplasts in the presence of rather large 

 amounts of PPNR. This is shown in figure 1. It can be seen that only when 



40- 



35- 



<u 30 



C23230 



/ 



A D D I T 1-0 N S 



I PPNR and cyh f"" 



I PPNR cyK f°'< and Flpr. 



m PPNR ± Flpr. 



yt.f. reduclion 



T 1 ^ 1 1 1 1 ' 



10 20 30 40 50 60 70 80 90 100 110 120 seconds 

 ILLUMINATION TIME 



Fig. 1 - TPN and cyt. f_ photoreduction. Tris buffer 0. 05 M, pH 8. 0; 

 MgCl2 0.005 M; ADP 0.003 M; Pi 0.005 M; TPN lO'^ M. 

 New-Zealand spinach (Tetragonia) chloroplasts containing 

 ITy of chlorophyll. Final volume: 1 ml. Additions: cyt. f°^ 

 21 and, respectively 16 mfimoles; flavoprotein 0.9 units 

 (0.9 /xmoles of ferricyanide reduced per minute) PPNR 

 0,05 ml. Light: 20. 000 Lux. 



