558 



M. ISHIMOTO AND F. EGAMI 



welchii. In this case, the presence of cytochrome has been observed and the 

 enzyme systems seem to be quite different [ii]. 



Table 3 

 Incorporation of ^-V]phosphate coupled with nitrate reduction 



Nitrate reduction to nitrite was observed in cotyledons of germinating bean 

 seeds Vigna sesquipedalis, which are actually under anaerobic conditions. The 

 nitrate-reducing enzyme system may resemble that of Clostridium judging from 

 the lack of reactivity with cytochrome present in the same tissues [12]. 



Nitrate reduction of this type may cause the substrate oxidation and promote 

 energy yielding in anaerobiosis (nitrate fermentation). 



Recently, in the early course of development of the frog a predominant 

 activity of nitrate reduction was found in the transient stage from glycolysis to 

 respiration [13]. 



The common character of these systems of nitrate reduction for energy supply 

 is the fact of the complete inhibition by oxygen, and in this respect differs from 

 those for assimilation. In the germinating stage of bean seed, the conditions of 

 the cotyledons are anaerobic and favour the dissimilatory reduction of nitrate to 

 nitrite and on the other hand, in seedlings assimilatory nitrate reduction proceeds 

 beyond nitrite in aerobiosis. 



By analogy with nitrate-reducing systems, enzyme systems for sulphate 

 reduction in Desulfovibrio are also considered to consist of reductase, dehydro- 

 genase and intermediary hydrogen carrier. The kind of cytochrome present in 

 this type of bacteria, in spite of its strictly anaerobic nature, is quite different. 

 This cytochrome was discovered by Postgate [14] and by Ishimoto [15] inde- 

 pendently. It has absorption maxima of a-band at 553 m/u and a very low redox 



