PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 349 



being specifically associated with chloroplasts* [77]. Moreover, Martius 

 and others have recently assigned a role to vitamin K in oxidative phos- 

 phorylation [82, 83; cf. 84, review; 85]. 



Apart from the catalytic efl:ect of FMN and vitamin K (and TPN ; cf. 

 [86, 87]), photosynthetic phosphorylation may also be increased by the 

 addition of non-physiological cofactors [74; cf. [88, 89]. Among these of 

 particular interest is phenazine methosulphate, since this dye is known to 

 be a strong reducing agent for cytochromes [90]. Phenazine methosulphate 

 was found to stimulate photosynthetic phosphorylation in bacterial 

 preparations by Geller [66] and Kamen and Newton [67] and in spinach 

 chloroplasts by Jagendorf and Avron [74]. 



COFACTORS OF BACTERIAL PHOTOPHOSPHORYLATION 



Of the cofactors of photosynthetic phosphorylation discussed so far, 

 ascoibate and phenazine methosulphate were found to be effective in 

 photosynthetic phosphorylation by cell-free preparations from RJiodo- 

 spirillum ritbntm [66] and C/iroiiuitiiint [67]. In addition, Geller [66] has 

 also found a stimulatory effect of vitamin K3. 



Under our experimental conditions photosynthetic phosphorylation by 

 cell-free preparations of C/ironiatiiini showed no response to added co- 

 factors when the particles were freshly prepared under anaerobic conditions. 

 On ageing, however, an effect of added vitamin K and phenazine metho- 

 sulphate was observed (Table I) ; the joint addition of these two cofactors 

 gave a greater increase of phosphorylation than when they were added 

 singly. The addition of FMN gave no increase [66, 67] and in fact, under 

 our experimental conditions often inhibited photosynthetic phosphoryla- 

 tion by Chromatium particles. 



Table II shows that photosynthetic phosphorylation by Chromatium 

 particles also resembled that of chloroplasts in its resistance to inhibition by 

 dinitrophenol, o-phenanthroline and antimycin A (when phenazine metho- 

 sulphate was present in the reaction mixture [cf. 66]) and its sensitivity 



* Bishop, who earlier presented evidence that vitamin K is an essential factor 

 for the photochemical activity of isolated chloroplasts [78], has reported in a more 

 recent publication [79] that spinach chloroplasts do not contain naphthoquinones 

 of the vitamin K type but contain instead the benzoquinone Q-255 ("plastoqui- 

 none "), which Crane [80] and Folkers and his associates [81] found in green 

 tissues and which Crane also found to be specifically concentrated in chloroplasts 

 [80]. Bishop [79] has reported that Q-255 activ'ates the Hill reaction. The role of 

 Q-255 in photosynthetic phosphorylation is still unknown, but it should be noted 

 that from the standpoint of the mechanism of photosynthetic phosphorylation 

 (see next Section), either a naphthoquinone of the vitamin K type or a benzoqui- 

 none would appear suitable as an electron carrier in the process. A clarification of 

 the disagreement between the earlier reports of vitamin K distribution in chloro- 

 plast [77] and the recent reports on Q-255 will be awaitetl. 



