Electron Transfer in Nitrate and Sulphate Respiration 



393 



electron transfer from the cytochromes to corresponding terminal electron 

 acceptors had been scarcely investigated on the enzyme level till the 

 symposium. 



The present paper describes the recent results obtained in Egami's labora- 

 tories by Taniguchi, Ohmachi and Itagaki and by Ishimoto and Fujimoto 

 on the terminal electron transfer in nitrate respiration and sulphate respiration 

 respectively. 



NITRATE RESPIRATION 



Cytochrome b^ and Nitrate Respiration 



A highly active nitrate-reducing system of nitrate respiration type was 

 found in E. coli grown in anaerobiosis with nitrate. As shown in Table 1, 

 anaerobic cells had very little activity in the aerobic reduction of nitrate. A 

 remarkably opposed tendency could be seen in cells grown aerobically in 

 the same medium with nitrate. They exhibited aerobic reduction much more 

 than anaerobic reduction (Table 1).* 



Table 1. Nitrate-reducing activity NaR of E. coli cells* 



Reaction mixture contains 100 /(moles of KNO3, 1 //mole of formate, 240 //moles of phosphate buffer. 

 pH 71, and E. coli cells in total volume of 3-0 ml. Temperature: 30°C. 



t In Warburg vessels under vigorous shaking. 

 J In Thunberg tubes under anaerobic conditions. 



The addition of nitrate in the anaerobic culture stimulates not only the 

 bacterial growth but also the cytochrome b^ content of the cells to the extent 

 of 2 to 3 times higher (almost to the same level as that of aerobic cells) as 

 compared with that of cells grown in anaerobiosis without nitrate. 



* Abbreviations 



The following abbreviations have been used in this paper: nitrate reductase, NaR 

 cytochrome, cyt.; formate dehydrogenase, FDH; /)-chloromercuribenzoate, PCMB 

 reduced methyl- or benzylviologen, MVH or BVH; phenazinemethosulphate, PMS 

 methylene blue, Mb; flavin adenine dinucleotide, FAD; flavin mononucleotide, FMN 

 adenosine-5'-phosphosulphate, APS; 3'-phosphoadenosine-5'-phosphosulphate, PAPS 

 adenosine triphosphate, ATP; 2-heptyl-4-hydroxyquinoline-N-oxide, HOQNO; diphos- 

 phopyridine nucleotide, DPN; reduced di- or tri-phosphopyridine nucleotide, DPNH or 

 TPNH; 2-amino-2-hydroxymethylpropane-l :3-diol, Tris. 

 I) 



