THE ELECTRON TRANSFER FROM 



CYTOCHROMES TO TERMINAL ELECTRON 



ACCEPTORS IN NITRATE RESPIRATION AND 



SULPHATE RESPIRATION 



By F. Egami, M. Ishimoto and S. Taniguchi 



Department of Biophysics and Biochemistry, Faculty of Science, 



University of Tokyo, Tokyo, and Department of Chemistry, Faculty of 



Science, Nagoya University, Nagoya 



Until 1949 the cytochrome system was considered to participate only in the 

 electron transfer to oxygen. The participation of a cytochrome in anaerobic 

 oxido-reduction was first suggested by Sato and Egami (1949) in the case of 

 nitrate reduction in E. coli. Recently a cytochrome was found even in a 

 strict anaerobe, Postgate (1954) and Ishimoto, Koyama and Nagai (1954a, b) 

 independently demonstrating the participation of a cytochrome in the 

 reduction of sulphur compounds in Desulphovibrio desiilphuricans. 



Nitrate reduction with participation of a cytoclirome system has been 

 called by us 'nitrate respiration', because its physiological meaning is not 

 nitrogen assimilation, but energy-yielding through oxido-reduction similar 

 to aerobic respiration (Sato, 1950; Taniguchi, Sato and Egami, 1956). The 

 electron transport mechanism functioning in such processes also appears to 

 resemble that of aerobic respiration. It has been shown that the electron- 

 transferring system in nitrate respiration in E. coli resides on particulate 

 structures containing cytochrome b-^ as in the case of the analogous system 

 involved in aerobic respiration. On the other hand, enzyme systems of 

 different nature in soluble form without participation of cytochromes have 

 been shown to be responsible for the reduction of nitrate in 'nitrate assimi- 

 lation' (Nason, 1956). 



Similarly sulphate reduction in Desulphovibrio desulphur leans, being an 

 energy-yielding mechanism with participation of cytochrome C3, may be 

 called 'sulphate respiration'. 



Our studies on the mechanisms of enzymic electron transfer in nitrate 

 respiration and sulphate respiration until 1957 were summarized by Tani- 

 guchi, Asano, lida, Kono, Ohmachi and Egami (1958) and Ishimoto, Kondo, 

 Kamayama, Yagi and Shiraki (1958) respectively at the International 

 Symposium on Enzyme Chemistry held in Tokyo in 1957. However, the 



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