REDUCTASE 91 



blades of young leaves and immediately behind the stem tips 

 in carbohydrate high plants three or four days after nitrate 

 had been supplied to the soil. Never was the process of 

 reduction affected by the presence or absence of light, and in 

 these experiments an activator such as acetaldehyde was not 

 used. From these observations it would appear that the 

 degree of activity of the " reductase " is much affected by the 

 reaction of the medium and that possibly sugar takes the place 

 of acetaldehyde. The process is thus brought closer to natural 

 conditions, but the best results were obtained at unnaturally 

 high temperatures. 



In an attempt to correlate the action of the potato " re- 

 ductase " with the aldehydase responsible for the reduction 

 of methylene blue to the leuco compound (see p. 139), Michlin * 

 and Bernheim f made preparations of the " reductase " of the 

 potato, the former by the precipitation by acetone from an 

 aqueous extraction and the latter by precipitation by ammon- 

 ium sulphate, dissolving in water, and treatment with charcoal ; 

 after which the enzyme was precipitated by saturation with 

 ammonium sulphate, centrifuged, dried in a vacuum desic- 

 cator and dissolved in water as required. Bernheim found 

 his preparation to have a wide p¥i range, 3 to 8-6, with an 

 optimum at 5-5, with respect to nitrate reduction ; at pH 7 to 

 7-5 there was a good nitrate reduction, in the presence of acet- 

 aldehyde, which corresponds sufficiently closely with Eckerson's 

 observations. J The action of the enzyme is independent of 

 traces of iron, as is indicated by the addition of KCN. Bern- 

 heim finds that there is a close relationship between this 

 potato aldehydase and typical aldehydase of animal origin, 

 the hitherto assumed difference between them disappearing 

 when the pH is adjusted. 



In the reaction, on Wieland's thesis (see p. 138), nitrate 

 is the hydrogen acceptor, and in these test-tube experiments 

 aldehyde is the hydrogen donator ; in the plant some other 



* Michlin : " Biochem. Zeit.," 1927, 185, 216. 



f Bernheim : " Biochem. Journ.," 1928, 22, 344. 



I It is to be remembered that the optimum reaction varies with the 

 degree of purity of the enzyme and upon the nature of the substrate (see 

 Vol. I., p. 468)." 



