138 PLANT RESPIRATION 



It is thus evident that malic acid in plant cells can be oxidised 

 to CO2. The combustion of oxalic acid is even more easily 

 accomplished. Zaleski and Reinhard^ found in plants a specific 

 enzyme which oxidises oxalic acid. Then Staehelin^ showed 

 that this enzyme is very widely distributed in the plant king- 

 dom. Although the plant acids could doubtless be burned to 

 CO2 and HoO it would be hasty to conclude that this process 

 of oxidation represents the final phase of normal oxygen res- 

 piration. Above all it is to be observed that the common 

 plant acids could be formed from amino acids as well as 

 from sugar. 



Since deaminization has been recognized as a widespread proc- 

 ess we know that the cleavage products of proteins may be 

 regarded as parent substances of various nitrogen free plant 

 materials. The author of this book considers that he can 

 assume that the common plant acids represent either trans- 

 formation products of amino acids, or either normal or by-prod- 

 ucts of incomplete change of sugar to amino acids in the case of 

 the synthesis of proteins. 



Such a strongly oxidised substance as oxalic acid can of course 

 be derived from protein as well as from sugar. It is known, 

 for one thing, that a considerable amount of oxalic acid is 

 formed in the treatment of proteins with nitric acid. Wehmer^ 

 showed that some molds produce enormous quantities of oxalic 

 acid at the expense of sugar, yet this investigator refers expressly 

 to the fact that part of the oxalic acid is formed not from sugar 

 but from protein substances. It also appears that oxalic acid 

 is formed in fungus cultures with peptone as the sole nutrient.* 

 From single amino acids as the sources of carbon the same 

 product was observed. According to some unpublished 

 experiments, Aspergillus niger produces oxalic acid in the 

 synthesis of protein from sugar and nitrates. Also the copious 

 formation of oxalic acid in the case of the regeneration of pro- 

 tein from asparagine in seed-plants is nothing but a result of 



' Zaleski, W. und Reinhard. Biochem. Z. 33: 449. 191 1; Palladin, W. und Lowt- 

 schinowsky. Mitt. d. Akad. d. Wiss. Petersburg. 1916: 937. . 



= Staehelin, M. Biochem. Z. 96: 1-49. 1919. 



3 Wehmer, C. Hot. Zeitschr. 49: 233. 1891; Bar. d. hot. Ges. 24 : 381. 1906; Zentralbl. 

 f. Bakt.. Parasitenk. u. Infektionskrankh. (II). 3: 102. 1897. 



» Butkewitsch, W. Biochem. Z. 129: 445. 1922. 



