396 



F. Egami, M. Ishimoto and S. Taniguchi 



* Activation. 



Nitrate reduction by the particulate system with formate as an electron 

 donor was strongly inhibited not only by CN- and N3-, but also by dicou- 

 marol, amytal and /7-chloromercuribenzoate (PCMB). This finding suggests 

 the participation of flavoprotein, dicoumarol-sensitive factor and SH group 

 besides heavy metals in the electron transfer sequence. On the other hand it 

 was activated by vitamin K3 and phenazine methosulphate (PMS) (Table 4). 



From these findmgs the following electron transfer sequence for the 

 particulate system can be proposed : 



Formatel 



DPNH I 



-^ (FAD) -> Cyt. bi 



Nitrate Reductase (NaR) ^ NO3 



t 

 MVH 



Phosphorylation Coupled with the Electron Transfer 



The decrease of inorganic phosphate was observed coupled with nitrate 

 reduction with formate as an electron donor by the particulate fraction 

 prepared with 2-amino-2-hydroxymethylpropane-l:3-diol (Tris) buffer 

 (0-02 M, pH 7-2). Adenosine triphosphate (ATP), glucose, yeast hexokinase, 

 Mg++ and F~ were added in the reaction mixture besides inorganic phosphate. 

 Glucose was scarcely utilized as an electron donor. It was found that the 

 particulate fraction itself contained ATP-ase which was activated by Mg++ 

 and inhibited by F-. 



The decrease of inorganic phosphate during the nitrate reduction indicates 

 the occurrence of an anaerobic phosphorylation coupled with the electron 

 transfer from formate to nitrate through cytochrome h^. These experiments 

 are still in a preliminary stage and the fate of phosphate incorporated 

 remains to be elucidated. 



