OXIDATIVE MECHANISMS 39 



of rupturing the bacterial cell-wall has niade the study of 

 cell-free bacterial enzymes a matter of considerable difficulty. 

 However, using the recently invented methods of breaking 

 bacterial cells by grinding with glass particles, shaking with 

 minute glass beads, exposure to supersonic vibration, etc. 

 (see p. 30), it has been possible to obtain a number of 

 dehydrogenases in a cell-free state and they do not appear to 

 differ significantly from their counterparts in other cells. 

 Amongst the enzymes isolated from Esch. coli we have those 

 which will specifically dehydrogenate formic acid to COg, 

 L-malic acid to oxalacetic acid, ethyl alcohol to acetaldehyde, 

 triosephosphate to phosphoglyceric acid, succinic acid to 

 fumaric acid, etc. The action of the dehydrogenase can be 

 written 



AHg = A H- 2H, 



and the dehydrogenation cannot take place until a hydrogen 

 acceptor B is available: 



AHg + B = A + BH2. 



The dehydrogenases are specific towards the hydrogen acceptor 

 as well as towards the substrate. In some cases the hydrogen 

 acceptor is oxygen, in which case the reaction is either 



AH2 + O2 = A + H2O2 or AHg + = A + HgO, 



but we find in practice that only relatively few dehydrogenases 

 can utiHse oxygen as hydrogen acceptor. An example of 

 such an enzyme is the D-amino-acid oxidase of animal tissues 

 which reacts 



K.CHNH2.COOH + > R.C:NH.COOH -f HgO, 



followed by spontaneous hydrolysis of the imino-acid to the 

 corresponding keto-acid with liberation of ammonia. 



The majority of the dehydrogenases effect a transfer of 

 hydrogen from the substrate to an intermediate carrier 

 represented by B in the above equation. The investigation 

 of such oxidation-reduction reactions has been carried out 



