CHAPTER II 



DEPARTURE FROM THE BIOSPHERE 



The earth and the surface waters are the natural tombs of plants and 

 animals. In these regions of the lithosphere and hydrosphere, the materials 

 of the biosphere return to the inorganic world : the nitrogen of proteins 

 becomes ammonia and nitrate, carbon is oxidized to carbonates and the 

 other elements return to their inorganic forms. Elsewhere, too, living 

 organisms are returning these elements by a continual rendering of respira- 

 tory carbon dioxide and metabolic excreta. The excreta and corpses are 

 mineralized in the soil and in water by the action of micro-organisms. 

 The latter, likewise, autolyse when unfavourable conditions interrupt their 

 multiplication. 



Particularly important are the processes by which nitrogen and carbon 

 leave the biosphere to re-enter the inorganic world. 



I. AMMONIFICATION IN THE SOIL 



The dead bodies and excreta of living beings are attacked in the ground 

 by the exoenzymes of many bacteria. For example, the exoenzymes of 

 many Clostridia attack this dead matter and the proteins are converted to 

 amino acids. Many bacteria release ammonia from these amino acids. 

 The most active ammonifying organisms are Bacillus mycoides, Proteus 

 vulgaris and various actinomycetes. Quantitatively the most important 

 process is oxidative deamination (p. 210). 



The bacteria of the soil can also accomplish a deamination by the 

 removal of ammonia to produce a double bond 



R_CH2— CHNH2— COOH -^ R— CH = CH— COOH -f NH3 



In this way bacteria of the coK-typhosum group can convert histidine to 

 urocanic acid. 



CH==CH— CH2CHNH2COOH CH=:CH— CH=CHCOOH 



I I 



HN N -^ HN N -t-NHs 



\ / \ // 



C C 



H H 



Histidine Urocanic acid 



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