44 BACTERIAL ENZYMES 



that catalase can also catalyse the oxidation of certain sub- 

 strates utilising HgOg as hydrogen acceptor, 



Catalase 

 AH2 + H2O2 > A + 2H2O. 



Such a reaction is said to be a " coupled oxidation " and the 

 result is again the removal of hydrogen peroxide. 



(6) Cytochrome systems: substrate type Sg, Table III. 



The formic dehydrogenase of Esch. coli belongs to this class. 



H.COOH + Cytochrome »► CO2 + Reduced Cyt. 



dehydrog- ^^^ 



enase ^ -^ 



^ ^ Cytochrome 



Reduced Cyt.+ -; >- Cytochrome + H,0 



' oxidase ' ^ 



The cytochrome system of animal- and yeast-cells consists 

 of at least three components which are distinguished by the 

 position of their absorption bands in the visual spectrum; 

 these components are known as cytochromes a, b, and c. 

 Cytochrome b is slowly autoxidisable but cytochromes a and 

 c cannot react with oxygen in the absence of cytochrome 

 oxidase. The cytochrome systems of bacteria differ from 

 those of animal- and yeast-cells in that bacteria may have 

 several or none of the components. Esch. coli has one com- 

 ponent only and this has absorption bands corresponding to 

 those of cytochrome b, but differs in that it is not autoxidisable ; 

 it is usually referred to as cytochrome b^. The distribution 

 of the cytochrome components as identified by their absorption 

 bands in various bacteria is given in Table IV: the letters 

 a, b, and c are given as for animal tissues, but it is by no means 

 certain that these bacterial cytochromes are identical with 

 those in other tissues. 



It can be seen from the table that certain species possess 

 no cytochrome components, and consequently cannot carry 



