208 BACTERIOLOGICAL CHEMISTRY 



suitable hydrogen doiiator (almost invariably a protein) 



is present : — 



GS G8H 



I + DH2 > + + D. 



GS GSH 



(protein) 



Thus glutathione acts as an intermediary in hydrogen 

 transfer from the donator to oxygen as acceptor in such 

 a way that hydrogen peroxide is not formed. 



It is very probable that glutathione is the prosthetic 

 group of the enzyme glyoxalase which brings about the 

 conversion of methylglyoxal to lactic acid (see p. 246) 

 by an internal dismutation : — 



CH3CO.CHO + H2O — > CH3CHOH.COOH . 



We have seen that when an organism grows in a 

 medium containing an organic compound as the source 

 of energy it usually oxidises that compound which accord- 

 ingly loses a certain amount of hydrogen. If the process 

 is aerobic the hydrogen is taken up by oxygen, but under 

 anaerobic conditions some substance other than oxygen 

 must act as the hydrogen acceptor. In order that it may 

 do so it must be activated by the organism concerned. 

 Aerobically only one compound, the hydrogen donator, 

 has to be activated, but anaerobically both donator 

 and acceptor have to be activated. If a medium 

 contains two compounds which can be activated in this 

 way (one as donator and one as acceptor) by an organism, 

 which is normally aerobic, it will support the anaerobic 

 growth of that organism, but not of an organism which 

 can activate only one or neither of the compounds. The 

 following examples illustrate this point. Each of the 

 organisms Esch. coli, Serratia marcescens, Proteus vulgaris 

 and Alcaligenes fcecalis has been shown by the methylene 

 blue technique to activate lactate as a hydrogen donator. 

 Both Esch. coli and Ser. marcescens can activate fumarate 

 and nitrate to act as hydrogen acceptors, and in conse- 

 quence these two organisms can grow anaerobically on a 



