40 BACTERIAL ENZYMES 



mostly with animal tissues or yeast-cells, so it will be best to 

 summarise the findings for enzymes from these cells and then 

 outline their application to bacteria. The general findings 

 are summarised in Table III. 



In animal tissues and yeasts the transfer of hydrogen from 

 substrate to oxygen passes through several intermediate 

 oxido-reduction reactions with oxygen as the final hydrogen 

 acceptor in the chain. 



AHj + B 



BH,+ C 



^enzyme 3 

 CH2+ D — - — ^C + DH2 



enzyme 4 



DH^+E >- D + EH2 



The ultimate carrier (D) is a haematin-protein called cyto- 

 chrome which is capable of alternate oxidation and reduction. 

 Eeduced cytochrome becomes oxidised again by the action 

 of the enzyme cytochrome oxidase. Oxidised cytochrome can 

 be reduced directly by the action of certain dehydrogenases 

 transferring hydrogen from their substrates to cytochrome. 

 The chain in this case (substrate type 83, Table III) can be 

 represented : 



/' AH2 ' 



A.H2 + Cytochrome > A + Reduced cytochrome 



dehydrogenase 



A Cytochrome ^^^^"^ 



Reduced cytochrome + > Cytochrome + H^O 



Oxidase 



The cytochrome is thus alternatively reduced by the action of 

 the dehydrogenase and oxidised by the action of cytochrome 



