484 



PRINCIPLES OF SOIL MICROBIOLOGY 



examples of this reaction, the transformation of leucine into isovaleric acid, 35 

 as shown above, of glutamic acid into succinic acid may be cited: 



HOOCCH 2 -CH 2 -CH-NH 2 -COOH + 2 = HOOC-CH 2 -CH 2 -COOH + NH 3 +C0 2 

 glutamic acid 



The decomposition of one amino acid may involve the reactions of oxidation, 

 deaminization, decarboxylation and reduction. The same organism may bring 

 about a series of these reactions, while different results may be obtained by the 

 same organism under different conditions. 



The transformation of tyrosine takes place according to the following reactions : 



OH OH OH OH 



+ H ' + NH 3 + + 3 ° CO, + H 8 O + 



CH 2 

 I 

 CH • NH 2 



COOH COOH 



Tyrosine p-Hydroxyphenyl- 



propionic 



acid 



(Hydroparacu- 



maric acid.) 



C0 2 + 



-f 30 



CH, 



p-Hydroxyphenyl- 



acetic 



acid 



p-cre- 

 sol 



OH 



H 2 + 



co 2 + 



COOH 

 p-Hydroxyben- 

 zoic acid 



Phenol 



Tyrosine may also be decomposed to homogentisic acid, ammonia and carbon 

 dioxide, as shown by Beijerinck 36 for an actinomyces. 



Aeration conditions have an important influence upon the nature of 

 the products formed from the decomposition of the amino acids. Prod- 

 ucts formed under aerobic conditions, such as hydroxy acids, may 

 prove unstable under anaerobic conditions, and vice versa. P-hy- 

 droxy-phenyl-propionic acid is formed from tyrosine under anaerobic 

 conditions; it is oxidized to p-cresol and phenol when air is admitted. 



The acids formed in the process of deaminization give rise to calcium 

 salts. These are broken down to carbonates and the ammonia is 

 oxidized to nitrates. The amines formed from decarboxylation are, 

 however, more resistant to bacterial action. In the case of optically 



35 Nencki, M. tTber den chemischen Mechanismus der Faulniss. Jour, prakt. 

 Chem., 17: 105-124. 1878. 



36 Beijerinck, M. VV. On the composition of tyrosinase from two enzymes. 

 K. Akad. Wetenschappen Amsterdam., 15: 932-937. 1913. 



