DEHYDRASE ACTION 67 



invoked to explain the reducing action of an aqueous extract of 

 potato. The existence of this was first demonstrated by Bach 

 in the following simple experiment. One gram of freshly 

 pounded potato is heated in a test tube to 60 C. with 10 c.c. 

 of 4 per cent aqueous solution of sodium nitrate together with 

 3 drops of 10 per cent solution of acetic aldehyde. After 

 two minutes the solution gives a strong reaction for nitrite by 

 the Griess Ilosvay reagent. The reduction of the nitrate to 

 nitrite was thought by Bach to be due to the activity of a per- 

 hydridase existing in the potato together with a per- 

 oxidase system. According to Wieland, however, this 

 is simply explained by the dehydrase activating the hydrogen 

 of the aldehyde hydrate whilst the sodium nitrate acts as 

 the hydrogen acceptor. 



^O x>H 



1. CH 3 cf + HOH = CH 3 C^-OH 



\H \H 



/OH yOH 



2. CH 3 C^-OH -> CH 3 C<f + 2 H 



\H ^O 



3. NaN0 3 + 2 H = NaN0 2 + H 2 O. 



Even the biological conversion of alcohol into acetic acid 

 by the vinegar plant, Bacterium aceti^ was shown by Wieland 

 to be a dehydrase action which could be effected in an atmos- 

 phere of nitrogen by leaving freshly washed cultures of the 

 plant in contact with alcohol and methylene blue in a flask 

 from which air had been displaced by nitrogen. In a com- 

 paratively short time the methylene blue was decolorized and 

 after some days a measurable quantity of acetic acid had been 

 produced.* 



There is thus considerable ground for regarding biological 

 oxidations as being primarily due to enzymes such as de- 

 hydrase which activate hydrogen in the oxidizable substances 

 so that it may be removed by a suitable hydrogen acceptor, 

 which may be atmospheric oxygen. Wherefore the oxidizable 

 substance is to be regarded as a potential hydrogen donator, 

 and, in fact, Thunberg f goes so far as to regard hydrogen as 

 the essential fuel of the living cell and regards only those 



* Wieland : " Ber. deut. chem. Gesells.," 1913, 46, 3336. 

 t Thunberg: Skand. Archiv. Physiol.," 1920, 40, i. 



5* 



