474 PRINCIPLES OF SOIL MICROBIOLOGY 



out forming free amino acids, but form groups (albumoses, peptones, 

 peptides) of lower amino acid content. Other enzymes, like trypsin 

 and erepsin, split the protein molecule more completely, bringing about 

 the formation of free amino acids. Still other enzymes (desamidases, 

 deaminases) act upon the amino acids and acid amides liberating 

 ammonia. 



The degradation of proteins by microorganisms proceeds along the 

 general lines of that produced by acids or proteolytic enzymes. A 

 further transformation of the protein derivatives takes place, however, 

 with the production of various secondary decomposition products, such 

 as ammonia and carbon dioxide, as well as amines, fatty acids, alcohols, 

 aldehydes, methane, phenol, indol, skatol, hydrogen sulfide, etc. Am- 

 monia which is so important, both from the point of view of the me- 

 tabolism of microorganisms and soil fertility, is usually formed as a 

 secondary decomposition product of the proteins; usually the amino 

 acid is used thereby as a source of energy. 



In some cases proteins form compounds with nucleic acids, giving 

 nucleo-proteins (or protein nucleates). These compounds are present 

 to a limited extent in all plants, animals and microorganisms, and are 

 thus introduced into the soil. On hydrolysis, a nucleo-protein is 

 transformed into an albumin (histone) and nuclein; the nuclein is 

 further hydrolyzed to albumin and nucleic acid. The protein, or 

 albumin, is decomposed by the microorganisms into albumoses, pep- 

 tones, amino acids and ammonia. The presence of these substances 

 in the soil has actually been demonstrated. 6 Often several groups of 

 organisms take part in the process; some break down the protein 

 to amino compounds and others utilize the latter and form ammo- 

 nia, as shown later. This is again comparable to the action of the 

 different groups of enzymes. 



The nucleic acids consist of C, H, O, N and P, in various propor- 

 tions, depending on the source of the acids. The composition of 

 nucleic acid from wheat is given as C4JL31O31N16P4; that of yeast, 

 C 36 H480 3 oNi4P4. The dissociation products vary with the source of the 

 acid; those of plant origin are phosphoric acid, guanine, adenine, cyto- 



• Walters, E. H. The presence of proteoses and peptones in soils. Jour. 

 Ind. Eng. Chem., 7: 860. 1915; Lathrop, E. C. The organic nitrogen com- 

 pounds of soils and fertilizers. Jour. Frankl. Inst., 183: 169-206, 303-321, 465- 

 498. 1917; Shorey, E. C. The isolation of creatinine from soils. Jour. Amer. 

 Chem. Soc, 34: 99-107. 1912; Nucleic acids in soils. Science, 35: 390. 1912; 

 Some organic soil constituents. Bur. Soils, U. S. Dept. Agr. Bui. 88. 1912. 



