276 EXISTENCE OF A REDUCING ENDO-ENZYME 



It would seem to be the ferment which starts the process 

 of internal respiration, oxidase that which continues and 

 completes it. 



IX. The Chemical Powers of Reductase. 



In conclusion I should like to point out the true reducing 

 character of the reductase of animal tissues. 



(a) In the first place it is a typical deoxidizer in that it 

 removes oxygen from osmium tetroxide and from such sub- 

 stances as oxyhaemoglobin, which is fully reduced, and 

 methaemoglobin, which is reduced to the oxy condition. 



(b) Substances containing oxygen, but not in a form 

 wholly removable, can be reduced from the higher to the 

 lower state, as when sodium nitrate is reduced to sodium 

 nitrite, (2^) or when sodium indigo-disulphonate and sodium 

 alizarine-sulphonate are respectively reduced to their pale 

 chromogens. 



(c) The reductase can also reduce metallic salts con- 

 taining no oxygen from their higher to their lower forms, as 

 when ferric chloride is reduced to ferrous chloride (^"). Here 

 the change involved is the removal of an ionic charge from the 

 trivalent ferri-ion which becomes the di-valent ferro-ion. 



(d) Finally, certain pigments containing no oxygen 

 such as soluble Prussian blue and methylene blue are reduced 

 to the pale or white chromogenic conditions of the di-potassio- 

 ferrous-ferrocyanide and methylene white respectively. 



In all these reductions, the endo-enzyme is behaving 

 after the manner of an inorganic reducing agent in an alkaline 

 medium. 



[The expenses of this research were met by a grant 

 from the Government Grants Committee of the Roj^al Society, 

 which is hereby gratefully acknowledged.] 



