ANTHONY SAN PIEIRO G39 



TABLE 4 



Effect of Photosynthetic Pyridine Nucleotide Reductase (PPNR) on 



TPN Reduction and Photosynthetic Phosphorylation 



Each reaction mixture contained 40 ^iTioies of Tris buffer, pW 7.8, 5 /imolcs of 

 potassium phosphate, pW 7.8, 10 /zmolcs of Me;Cl-2, 70 ^moles of NaCl, 8 imolcs of 

 .^DP adjusted previously to pH 7.8, 4.5 ^imolcs of TPN, chloroplasts equivalent to 

 124 micrograms of elilorophyll, and, where indicated, 20 units of enzyme. Final volume 

 was 3 ml. Illumination for 10 minutes at 22°C. 



Decrease in 

 PPNR TPNH formed, inorganic phosphate 



/imoles Atmoles 



- 0.4 0.2 



+ 2.6 1.3 



^\•ashed green particles restored to the particles the capacity for 

 photosynthetic phosphorylation. 



Photoinactivation 



Initial studies of the photosynthetic reduction were complicated 

 by the observation that the rate of TPN reduction rapidly decreased 

 with time. It was shown subsequently that the non-linearity of TPN 

 reduction is the result of a chloroplast-dependent photoinactivation 

 of PPNR (12) . In the presence of a number of reducing compounds 

 as well as ferricyanide, the photoinactivation is prevented and the 

 reduction of TPN proceeds linearly. 



Physical Properties 



The purified enzyme is reddish-brown in color. An absorption 

 spectrum of the enzyme is shown in Fig. 3. The wavelengths of the 

 maxima are 278, 327, 420, and 460 m^.. There is a shoulder at 290 

 m^. To date it has not been possible to associate these spectral charac- 

 teristics with any of the usual electron-transport compounds. While 

 the nature of the redox group, if any is present, in the protein is 

 luiknown, it does not appear to be either a haem or a flavin. 



It should be noted that the ratio of the absorption at 280 and 260 

 m^ is only 1.2. 



The enzyme was found to give a single symmetrical peak in the 

 Spinco Ultracentrifuge and Tiselius Electrophoresis. The molecular 

 weight of the enzyme, in jDreliminary experiments, was found to be 

 about 15,660 from sedimentation and diffusion data as well as by the 

 Archibald method. 



Amino acid analysis of the enzyme indicated a total of about 95 



