48 BACTERIAL ENZYMES 



reduction of B. Several such " coenzyme-linked " oxido- 

 reductions have been demonstrated in fermentation reactions 

 (Chap. VII). In the Clostridia we find an oxido-reduction 

 occurring between two amino-acids: 



E . CHNH2 . COOH K . CO . COOH 



+ H2O > + 2NH3 



X . CHNH2 . COOH X . CH2 . COOH. 



The enzymes in this reaction have not as yet been investigated 

 in detail, although it is possible to demonstrate the presence 

 of the specific dehydrogenases for K.CHNH2.COOH and 

 X.CHNH2.COOH (Chap. IX). The Methanobacteria carry 

 out an interesting oxido-reduction reaction, in which alcohols 

 are oxidised anaerobically with CO2 acting as the H-acceptor, 

 and being reduced to methane (p. 154). 



2CH3 . CH2OH + CO2 > 2CH3 . COOH + CH4. 



Hydrogenase: Many bacteria are able to activate 

 molecular hydrogen as H-donator by the possession of a potent 

 enzyme, hydrogenase, which catalyses the reaction: 



Hydrogenase 

 H2 --- --^ 2H. 



The presence of this enzyme can be demonstrated in Esch. coli 

 by shaking a suspension of cells with methylene blue in the 

 presence of gaseous hydrogen when the dye becomes reduced 

 and decolourised. Boiling of the organisms or replacing the 

 hydrogen by any other gas stops the reduction. In this 

 reaction methylene blue acts as H-acceptor for hydrogen 

 made available by hydrogenase and, similarly, other suitable 

 H-acceptors can be reduced in the presence of hydrogen. 

 Esch. coli possesses an enzyme, nitratase, which activates 

 nitrate as H-acceptor, so in the presence of the cells and 

 hydrogen, nitrate is reduced to nitrite: 



HNO3 + 2H > HNO2 -f H2O. 



The reduction does not stop at this point but continues all 



