l6o PHYSIOLOGY OF NUTRITION 



§5. Nitrogenous Products of Protein Decomposition.— Asparagin (NH2- 

 CO— CH2— CHNH2) is the most important product of protein decomposition in 

 plants. Germinated legumes that have been kept in the dark, especially Lupi- 

 nus Ititeus, are notably rich in this substance. According to Borodin,i asparagin 

 is not present in the Caryophyllacese, in which glutamin occurs, however. 

 Glutamin (NH2CO— CH2— CH2— CHNH2— COOH) is a product similar to 

 asparagin, but it is known only in isolated cases, since it is difficult to bring to 

 crystallization and gives no definite reaction. This substance is present in sugar 

 beets and is abundant in Curcurbita seedlings. It takes the place of asparagin 

 in the Caryophyllaceae and in ferns.^ 



The following amino acids and basic substances may be mentioned as other 

 products of protein decomposition in plants. 



MoNOAMiNO Acids 



Leucin, (CH3)2.CH— CH2— CHNH2— COOH. 

 Tyrosin, CeHjOH— CH2— CHNH2— COOH. 

 Valin, (CHs)^— CH— CHNH2— COOH. 



Basic Substances' 

 Lysin,NH2CH.— CH2— CH2— CH2— CHNH2— COOH. 

 NH2 

 NHCH2— CH2— CH2— CHNH2— COOH. 



Arginin, HN=C\ 



Histidin, /^^V 

 NH N 



CH = C— CH2— CHNH2— COOH. 



Large amounts of arginin are present* in conifer seedlings. The purin bases," 

 xanthin, hypoxanthin, adenin and guanin, the formulas for which are given 

 below, arise from the decomposition of the nucleo-proteins. 



■ Borodin, i88s. [See note i, p. isS.] 



' Schulze, E.,. Ueber die Verbreitung des Glutamins in den Pflanzen. Landw. Versuchsst. 48: 33-55. 

 1897- 



3 Schulze, E., and Winterstein, E., Ueber die bei der Spaltung der Eiweisssubstanzen entstehenden 

 basischen P rodukte. Ergeb. Physiol, i : 32-61. 1902. 



* Schulze, E., Ueber .die beim Umsatz der Proteinstoffe in den Keimpfianzen einiger Coniferen-Arten 

 entstehenden Stickstoflverbindungen. Zeitsch. physiol. Chem. 2a: 435-448. 1896-1897. 



" The purin bases may be considered as derived from purin, whicli is not found in nature, 

 but which has been synthetized. It may be represented as follows, the various atomic posi- 

 tions in the two rings being numbered. 



(i) N=(6) CH 



(2) CH (s) C— (7) NH\ 



II II, >(8) CH 



(3) N-(4) C-(9) N 



Referring to the numbers, xanthin is called 2-6-dioxypurin. Adenin is 6-aminopurin, hypo- 

 xanthin is 6-oxypurin, and guanin is 2-amino-6-oxypurin. — Ed. 



