66 RESPIRATION 



Wieland * also effected the oxidation of glucose to carbon 

 dioxide by shaking it with palladium black and methylene 

 blue at room temperature. He similarly effected the oxida- 

 tion of phenolic substances such as hydroquinone and pyro- 

 gallol to quinone and purpurogallin respectively in the entire 

 absence of oxygen, oxidations which, according to the Bach 

 and Chodat theory ,f are effected by atmospheric oxygen acti- 

 vated by an oxidase system. 



Wieland J also investigated the so-called Schardinger reac- 

 tion in milk. This reaction, designed by Schardinger to dis- 

 tinguish boiled from unboiled milk, depends upon the fact that 

 unboiled milk when warmed with methylene blue and a drop 

 of acetic aldehyde decolorizes the dye, whereas boiled milk 

 produces no such change. According to Wieland this action 

 is due to an enzyme, for which he proposes the name dehydrase ; 

 this enzyme dehydrogenates the aldehyde hydrate in the same 

 way as the palladium black, the methylene blue again acting 

 as hydrogen acceptor. The same enzyme is also able, by 

 slightly varying the conditions, to produce from two mole- 

 cules of salicylic aldehyde one molecule of the corresponding 

 acid and one molecule of the alcohol ; the latter being pro- 

 duced by one of the molecules of salicylic aldehyde itself 

 acting as the hydrogen acceptor. 



xOH~ /OH 



C 6 H 4 OH . CHO + H 2 -> C 6 H 4 OH . C^-OH -> C 6 H 4 OH . C^ + 2H 



\OH ^O 



A second molecule of salicylic aldehyde then acts as 

 hydrogen acceptor forming a molecule of salicylic alcohol 



C 6 H 4 OH . CHO + 2H -> C 6 H 4 OH . CH 2 OH. 



This change effected by enzyme activity of two molecules of an 

 aldehyde into one molecule each of the corresponding alcohol 

 and acid was originally thought by Parnas to be due to a 

 special enzyme to which he gave the name aldehyde mutase ; 

 Wieland's work, however, shows that this substance is none 

 other than dehydrase. This same enzyme dehydrase can be 



* Wieland : " Ber. deut. chem. Gesells.," 1913, 46, 3331. 

 tVol. I., p. 396. 



J Wieland: " Ber. deut. chem. Gesells.," 1914, 47, 2085. 

 Parnas : " Biochem. Zeitsch.," 1910, 28, 274. 



