I40 PLANT RESPIRATION 



(I)COOH— CHo— CH(NHo)— COOH + O = COOH— CHo— 



CO— COOH + NHs 



(II) COOH— CHo— CO— COOH = COOH— CHo— CHO + 



CO2 



(III) COOH— CHo— CHO + O = COOH— CH2— COOH. 



However, this process cannot take place because the oxala- 

 cetic acid COOH— CHo— CO— COOH is not split by carboxy- 

 lase in the same way as is a-keto-glutaric COOH — CH2 — CH2 — 

 CO — COOH. It has been shown experimentally that oxala- 

 cetic acid spHts off two rather than one molecule of COo, 

 whereby it is changed to acetaldehyde.^ 



Acetaldehyde is probably oxidised higher than acetic acid 

 or glyoxal to oxalic acid, which either remains as the end-prod- 

 uct of the cleavage of asparagine or most of it passes over into 

 COo and H2O. In some unpublished experiments Kostychev 

 has been able to form malic acid by the action of yeast since 

 COo is not split off because the carbonyl group is reduced to the 

 hydroxyl group before the carboxylase takes hold: 



COOH— CHo— CO— COOH + 2H = COOH— CHo— CHOH 



—COOH. 



The same reduction appears to be effected in the case of 

 some molds and possibly is not precluded in seed-plants under 

 certain conditions. In this way we are justified in assuming 

 that malic as well as oxalic acid can be formed from aspartic 

 acid. If malic acid is formed from sugar it is really not a stage 

 of the normal respiratory process but an intermediate phase of 

 the formation of asparagine. Actually an increased formation 

 of malic acid or malic acid monamide was demonstrated by 

 Schulow and Petrow- for germinating seed-plants. Prianischni- 

 kow and his students^ have also observed a considerable increase 

 in the amount of asparagine in seedlings after artificial feeding of 

 salts of malic acid. Still more interesting in this connection 

 are the pioneer studies in animal physiology by Embden and 



1 Neuberg, C. und L. Karczag. Biochem. Z. 36: 68. 191 1. 



2 Schulow, Iw. Untersuch. im Bereich der Physiol, der Ernahr. hoherer Pflanzen. 1913- 

 Russian; Petrow, G. G. loc. cil. 



8 Prianischnikow, D. Taeebuch d. I. KoiiKr. d. russ. Bot. 1921 : 65; Smirnow, A. Bio- 

 chem. Z. 137 : I. 1923- 



