254 



Keelin T. Fry and Anthony San Pietro 



similar data for the spinach ferredoxin isolated in Arnon's laboratory '^^' ^^\ 

 the red enzyme from Chlorella isolated by Gewitz and Volker (^^) and the 

 PPNR isolated from Japanese spinach by Horio and Yamashita ^^^> are in- 

 cluded. Except for the PPNR from Brassica and Japanese spinach, the values 

 at each wavelength for the various proteins are almost identical. These data 

 provide support for the hypothesis that the chromophoric group(s) responsible 

 for the visible absorption of these proteins is the same. 



It is interesting that the extinction coefficients per iron at 390 mp for the 

 Clostridial ferredoxins are approximately the same as those reported in 

 Table 1 for the absorption at 465 mp.. From the data of Buchanan et al. (^^' 

 one can calculate that the extinction coefficients of the Clostridial ferredoxins 

 at 390 mp per micromole of iron per milliliter are about 3. 5-4. 5 assuming a 

 value of 12, 000 for the molecular weight and an iron content of 10 atoms of 

 iron per mole. 



TABLE 1 



Correlation of Absorbance in the Visible Region and Iron Content 



The values are presented as the absorbance of a solution of protein containing 

 one micromole of iron per milliliter. 



f^Calculated from the lower curve in Fig. 1. 



Calculated from the data of Gewitz and Volker ^^^'. 

 ''Calculated from the data of Whatley, Tagawa and Arnon (^^) and 

 , Tagawa and Arnon ^^'*'. 



Calculated from the data of Bendall, Gregory and Hill ^'^> and the 

 upper curve in Fig. 1. 

 ^Calculated from the data of Katoh and Takamiya ^ ). 

 Calculated from the data of Horio and Yamashita ( ^ ^i assuming a 

 molecular weight of 14, 000. 



A MINO ACID COMPOSITION 



The amino acid composition of PPNR from spinach is given in Table 2. 

 The protein is acidic as evidenced by the high concentration of aspartic and 

 glutamic acids and the low concentration of the basic amino acids. 



