DANIEL I. ARNON 507 



Cofactors of Bacterial Pliotophosphorylatioi} 



Of the cofactors of photosynthetic phosphorylation discussed so far, 

 ascorbatc and j)henazine niethosulfatc, but not FMN, were found to 

 be effective in photosynthetic phosphorylation by cell-free prepara- 

 tions from RJiodospirilhim rubrum (59) and Chromatiuni (81) . In 

 addition, Gellcr (59) has also found a stimulatory effect of vitamin K3. 



Under oin^ experimental conditions photosynthetic phosphoryla- 

 tion by cell-free preparations of Chrotnathun showed no response to 

 added cofactors when the particles were freshly prepared under 

 anaerobic conditions. On aging, however, an effect of added vitamin 

 K and phenazine methosidfate was observed (Table 2) ; the joint 



TABLE 2 



Effect of Vitamin K5 and Phenazine Methosulfate (PMS) on 



Photophosphorvlation by Aged Cell-free Preparations of Chromatiitm 



[Chromatophores (P) and Supernatant Fluid (S)] 



(Ogata, Nozaki, and Arnon, 115) 



' P and S were stored separately in Treatments 1 and 2 and together in Treatments 3 

 and 4. 



Each vessel contained, in a final volume of 3.0 ml, cell-free preparation containing 

 0.3 mg bacteriochlorophyll, and the following in micromoles: Tris buffer, pW 7.8, 80; 

 MgClo, 5; K2H32PO4, 10; and ADP, 10. 0.1 //mole each of vitamin Ks (2-methyl-4- 

 amino-1-naphthol hydrochloride) and PMS were added as indicated. Gas phase was 

 argon. The reaction was carried out at 20°C for 30 minutes and stopped by adding 

 0.3 ml of 20 per cent trichloracetic acid TC.\ to each vessel. Illumination 3."},000 

 Lux. 



addition of these two cofactors gave a greater increase of phosphoryla- 

 tion than when they were added singly. The addition of FMN gave 

 no increase (59, 81) , and in fact, vmder our experimental conditions, 

 inhibited photosynthetic phosphorylation by Chromatiuni particles. 

 For the purposes of experimental analysis, bacterial photophos- 

 phorylation thus appeared to be of the vitamin K or phenazine 

 methosulfate type rather than of the FMN type (172) . This con- 

 clusion was confirmed by the response of Chromatium photophos- 

 phorylation to inhibitors, as shown in Talile 3. Photophosphoryla- 



