REDUCTION OF DINITROPHENOL BY CHLOROPLASTS 



TABLE II 



Catalytic Activity of Phenols ix Cyclic Photofhosphorylation 



445 



Active 



Inactive 



2,4-dinitrophenol 



2,5-dinitrophenoI 



2,6-dinitrophenoI 



2,4-dinitro-5-acetylaminophenol 



2-nitro-4,6-dimethylphenol 



2-nitro-4,5-dimeth\iphenol 



2-nitroresorcinoI 



o-nitrophenol 



w-nitrophenol 



/)-nitrophenol (slightly active) 



2-amino-4-nitrophenol 



^-nitrophenylphosphate 



picric acid 



2,4-dinitro-6-methylphenol 



2,4-dichlorophenol 



pentachlorophenol 



o-cresol 



p-cresol 



o-methoxyphenol 



o-aminophenol 



A«-arninophenol 



^-aminophenol 



^-acetylaminophenol 



o-phenolsLilphonic acid 



hydroquinone 



catechol 



(phosphate, ADP, MgCl^, gkicose and hexokinase) are present. The 

 reaction is strongly inhibited by lo^^ m o-phenanthroHne, 4 x io~'' m CMU, 

 and lO"^ M NH.,OH, which are known to inhibit the Hill reaction, and is 

 accompanied by oxygen production (nearly i ■ 5 jumole Oo/jumole of DNP). 

 The inhibition of the photoreduction of DNP by low concentrations of 

 NH2OH and o-phenanthroline may explain the finding that cyclic photo- 

 phosphorylation catalyzed by DXP is more sensitive to these poisons than 

 is photophosphorylation in the presence of ^•itamin K3, which apparently 

 is independent of the formation of molecular oxygen. 



The photoreduction of DXP is strongly stimulated by KCN, but even 

 under these conditions the rate is not higher than about 4 /xmoles DNP 

 reduced/mg. chlorophyll/hour. DNP reduction thus proceeds at a much 

 lower rate than the reduction of usual Hill oxidants, such as indophenol 

 dyes or ferricyanide. As 3 x io~^ molar /)-chloromercuribenzoate shows no 

 inhibitory effect, it seems unlikely that photoreduction of TPN, which is 

 very sensitive to this poison, is involved in the photoreduction of DNP. 

 It is known, on the other hand, that the Hill reaction is resistant to p- 

 chloromercuribenzoate. 



From these experiments we may conclude that the ability of DNP to 

 catalyze ATP synthesis by ilhmiinated chloroplasts is due to photo- 

 reduction of this compound. 



Photoreduction of DNP does not occur in the presence of phosphorylat- 

 ing reagents and vitamin K3 or FMN. This indicates that the conversion 

 of DNP into aminonitrophenol cannot account for the insensitivity of 



