BACTERIAL RESPIRATION 201 



related to haematin and distinguished by characteristic 

 bands in their absorption spectra. Cytochrome appears 

 to be present in all cells exposed to oxygen (with the 

 exception of some streptococci, e.g. Str. lactis). Cyto- 

 chrome can exist in the oxidised and in the reduced 

 forms containing iron in the ferric and ferrous forms 

 respectively : — 



Oxidised cytochrome v Reduced cytochrome. 



The oxidised form can act as a hydrogen acceptor in 

 presence of dehydrase (or dehydrogenase) enzymes giving 

 reduced cytochrome at the expense of the hydrogen of 

 the donator, DHg : — • 



+ Dehydrogenase 

 Oxidised cytochrome ^Redu?ed cytochrome + D. 



Reduced cytochrome can be re -oxidised by atmospheric 

 oxygen under the influence of cytochrome-oxidase with 

 production of water : — 



HgO 4- Oxidised cytochrome ^ — 



Oxidase 



Reduced cytochrc 



SO that in effect the whole system acts as a catalj^st, 

 bringing about the oxidation of the substrate, DHg, to 

 D and water : — 



DH2 



+ 



HoO + Oxidised cytochrome 



Dehydrogenase 

 =- Reduced cytochrome + D 



Oxidase 



Oo 



The first step, the reduction of oxidised cytochrome by 

 dehydrogenase, can be inhibited by narcotics like chloro- 

 form or the urethanes, so that in their presence there is 

 an accumulation of oxidised cytochrome. The second 

 stage can be inhibited by the action of cyanide or 

 sulphide, under whose influence reduced cytochrome 

 accumulates. 



