4 3 4 SCIENCE PROGRESS 



Recently Baudisch l has shown that daylight alone may 

 reduce nitrates in solution to nitrites, and that both nitrates 

 and nitrites are readily reduced by aldehydes in presence of light 

 with the ultimate production of ammonia and amino-compounds. 



In view of these possibilities, the aid of reducing enzymes or 

 reductases may not be necessary; on the other hand their pres- 

 ence may enable protein synthesis to continue in the dark. In any 

 case, the evidence is increasing that enzymes of specific or general 

 reducing activity are present in both plant and animal tissues. 2 



There are indications that reductases would be more fre- 

 quently met with in plant extracts if it were not for the presence, 

 in the same juice, of oxidising enzymes or oxidases. These two 

 types of enzymes may exist side by side in the same cell, and 

 both exert their full activity without interference, because their 

 respective spheres of action may be limited by living semi- 

 permeable membranes. In crushing the tissues to extract the 

 enzymes, these controlling membranes are destroyed, the two 

 enzymes come in contact, and the reductase may be destroyed or 

 its activity neutralised. 



The immediate result of the reduction of a nitrate in the 

 living cell must be the production of the very poisonous nitrite. 

 This body must be again transformed immediately or the death of 

 the cell will follow. It may therefore be very difficult to detect 

 the transitory appearance within the organism of the nitrite, and 

 thus establish the existence of a reducing action. On the other 

 hand, as we have seen, in experimenting " in vitro," there is the 

 difficulty of extracting the reductase in an active condition. 



Irving and Hankinson obtained evidence of the presence of a 

 nitrate-reducing enzyme in the plant by placing chloroformed 

 leaf tissue in a solution of asparagin and potassium nitrate. 



The sap of the plant was acid, and in an acid medium, if 

 nitrites are formed in the presence of asparagin, gaseous nitrogen 

 must be liberated. Thus — 



2HNO, + CH.NH 2 - COOH CH.OH-COOH 



I -> I + 2N 2 + 2H 2 



CH 2 - CONH 2 CH 2 - COOH 



(Asparagin.) (Malic acid.) 



1 Baudisch, Ber.deut. Chem. Ges. 44, p. 1009, 191 1. 



3 On animal reductases, see D. F. Harris and H. J. M. Creighton, Proc. 

 Roy. Soc. 85 B. p. 486, and Bioch. Journ. vi. p. 429. On plant reductases, see 

 Kastle and Elvove, Amer. Chem. Journ. 31, p. 606, 1904, and Irving and 

 Hankinson, Bioch. Journ,, vol. vii. p. 87. 



