104 BIOCHEMICAL SYSTEMATICS 



the same individual differed. Thus arginine was found to predominate 

 in the lower stem in ash (Fraxinus), but moving toward the stem 

 apex glutamic acid, asparagine, and glutamine in the order listed rep- 

 resented the main amino acids of corresponding positions. 



The three acids found in high concentration in the stem apex 

 (namely, glutamic acid, asparagine, and glutamine), plus asparatic 

 acid, are consistently among the predominant amino acids of nu- 

 merous plant species. These acids are probably among the first com- 

 pounds into which amino nitrogen is incorporated. Asparagine is the 

 amide of aspartic acid which, in turn is derived via transamination 

 from the Krebs' cycle acid, oxaloacetic acid. Similarly, glutamine is 

 an amide of glutamic acid, also derived via reductive amination of 

 another Krebs' cycle acid, a-ketoglutaric acid. 



Because of the metabolic position of these acids no special 

 significance is attached to their prominant occurrence in a large num- 

 ber of species. Therefore, statements such as that by Korohoda et al. 

 (1958) that glutamine, glutamic acid, and alanine are most character- 

 istic of the genus Brassica have very little systematic significance. 

 However, in certain cases less common amino acids appear to be con- 

 sistently prominent in a family and thus are characteristic of the 

 metabolism of that family. Some examples taken from Renter (1957) 

 are discussed below. It should be borne in mind, however, that rapid 

 changes in amino acid content may accompany development, and the 

 concept of "principal amino acid" should not be applied too vigorously. 



Arginine, illustrated below, possesses the guanidine group: 



R— NHCNH2 

 NH 



CH2NHCNH2 



NH 



CH2 



CH2 



CHNH2 



COOH 



Arginine is often present as a principal amino acid in the 

 families Saxifragaceae, Hamamelidaceae, and Rosaceae, but its occur- 

 rence elsewhere as a principal amino acid is sporadic. It is noteworthy 

 that other guanidine compounds are conspicuous in the family 

 Rosaceae (Reuter also reported the presence of certain guanidine 

 compounds) and in the one member of the family Hamamelidaceae 

 which was tested, namely, Parrotia persica. Only a few members of 

 the family Saxifragaceae were tested, and these were negative for 

 guanidines other than arginine. 



