DECOMPOSITION OF PROTEINS 475 



sine, thymine and laevulinic acid. Laevulinic acid is formed from a 

 hexose group in the molecule of the nucleic acid. The decomposition 

 of the nucleic acids takes place as follows: 7 



Zoo or Fhytonucleic acids 

 Nucleotides 



Phosphoric acid /\ Nucleosides 



Carbohydrate / \iBase and carbohydrate) 



complex 



J 



Base 

 (Purine or pyrimidine) 



Phosphoric acid 



Carbohydrate 

 (Pentose or hexose) 



Protein decomposition by microorganisms. The course of protein 

 decomposition by microorganisms can be followed in three different 

 ways. 



1. The disappearance of the protein. The residual protein is pre- 

 cipitated by means of an acid or alkali, by alcohol or other precipitating 

 agents or by heat. The protein is determined either by weighing the 

 dry precipitate or determining the total nitrogen in it. In the case of 

 peptone, the biuret test may be used 8 as a measure of its decomposition. 



2. The formation of intermediary products, such as peptones or 

 amino compounds. The first can be determined quantitatively by 

 the biuret reaction and the second by the Van Slyke method, 9 the 

 formol titration method, 10 or the Folin method. 11 



3. The formation of ammonia as the final product of protein 

 decomposition. 



Each of these three methods has its advantages and disadvantages. 

 By the first method, we determine the absolute amount of protein 

 decomposed, but we do not know how far the decomposition has pro- 



7 Levene, P. A. Partielle Hydrolyse der Nucleinsauren. Abderhald. Haadb. 

 Biochem. Arbeitsm., 2: 605-609. 1911; 5: 489-499. 1911. 



8 Berman, N., and Rettger, L. F. The influence of carbohydrates on the 

 nitrogen metabolism of bacteria. Jour. Bact., 3: 3S9-402. 1918. 



9 Van Slyke, 1913-14 (p. 473). 



10 Sorensen, S. P. L. Enzymstudien. I. Biochem. Ztschr., 7:45. 1907. 

 11 Folin, O. A new colorimetric method for the determination of amino acid 

 nitrogen in blood. Jour. Biol. Chem., 51: 377-391. 1922. 



