BACTERIAL RESPIRATION 207 



tlie bottom of the hold was reached. The cargo would 

 all be transferred from the deck to the hold but no sack 

 would have to be moved through more than a small 

 distance-. The cargo obviously represents hydrogen 

 atoms, the sacks are the enzymes, the different levels 

 are the different co -enzymes, the deck is the substrate 

 and the hold represents atmospheric oxygen. 



The autotrophic hydrogen bacteria contain a hydro - 

 genase by which the reduction of such substrates as 

 oxygen, nitrate, sulphate or fumarate by molecular 

 hydrogen is effected, a process very similar to reduction 

 by hydrogen in presence of platinum black as a catalyst. 



It is possible to induce many anaerobes to grow in the 

 presence of oxygen by causing the medium to have a 

 reducing potential sufficiently high to overcome the 

 effect of the oxygen and prevent the formation of hydrogen 

 peroxide. This can be accomplished by the addition of 

 strongly reducing substances like cystein or the oxidation- 

 reduction system glutathione, both of which contain the 

 sulphydryl group ■ — 8H. Glutathione is a tripeptide 

 ( Y-glutamylcysteylgiycine) comj)osed of glycine, cystein 

 and glutamic acid : — 



COOH.CH.CH2.CH2.CO. 



NH.CH.CO. NH.CHo.COOH 



I 

 CH2 



L 



(glutamic acid) (cystein) (glycine) 



Its formula is usually written in brief as GSH. 



Two molecules of this reduced form of glutathione can 

 combine with elimination of hydrogen to give the oxidised 

 form : — 



The oxidised form can be readily reduced again if a 



