PHOTOSYNTHETIC PHOSPHORYLATION IN THE PRESENCE 

 OF NATURALLY OCCURRING SUBSTANCES 



C. C. Black and A. San Pietro 



After the initial observation of photosynthetic phosphorylation i^'^i it 

 was demonstrated that many common laboratory redox chemicals support 

 photophosphorylation. A list of these chernicals would include: methyl 

 phenazonium methosulfate, or pyocyanine ^3-5). ferricyanide ^6); viologen 

 dyes (^' ''' ^); anthraquinone ^^'; dimethyl safranin sulphonate '^^>; methylene 

 blue (5); indigo carmine (^); and indophenol dyes (9-i2)_ -phe natural occur- 

 rence, hence physiological role, of these chemicals is doubtful. The 

 following substances occur naturally, may have a role of physiological 

 importance, and have been shown to support photophosphorylation: vitamin 

 K "13). FMN (1^): riboflavin (l^); NADP (^'^^^ plastoquinone ^ 'l. 

 allagochrome (i^h a "flavone- type" compound (^^): cytochrome c ^ ^>; and 

 photosynthetic pyridine nucleotide reductase (PPNR)^^"^ . Although these sub- 

 stances occur in nature and may play a physiological role, it appears that 

 they are involved in the electron transfer pathway rather than the phosphory- 

 lation process. 



Since scant experimental data was available concerning the components 

 involved in the phosphorylation mechanism, research was undertaken to 

 isolate a naturally occurring substance or substances involved in photophos- 

 phorylation. Evidence will be presented which indicates that we have 

 successfully obtained a new naturally occurring catalyst of photosynthetic 

 phosphorylation. The catalyst(s) has been detected in all types of photo- 

 synthetic organisms, and the catalyst from one organism has been shown to 

 initiate photophosphorylation with both chloroplast and chromatophore frag- 

 ments. We have tentatively assigned the name phosphodoxin to the catalyst. 



ISOLATION AND DISTRIBUTION 



Acetone powders of intact spinach chloroplasts were the first source 

 of phosphodoxin ^^^\ We soon learned that phosphodoxin was not destroyed 

 by heating at 100° C for periods up to 30 minutes; therefore, whole leaves 

 or whole cells extracted with boiling water proved to be convenient sources 

 of phosphodoxin. Most of the work in this paper will deal with spinach phos- 

 phodoxin since it has been studied more exhaustively than phosphodoxin from 

 other photosynthetic organisms. More extensive data relating to the activity 

 of phosphodoxin isolated from photosynthetic bacteria can be obtained in 

 references 21 and 22. A partial list of the photosynthetic organisms in 

 which phosphodoxin has been detected is given in Table 1, along with the 



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