AMINO ACIDS 105 



Citrulline, as indicated by its formula, is closely related to 

 arginine. It was originally reported in the family Cucurbitaceae and 

 is present in several members of the family. It rarely appears in 

 Reuter's table except in the families Juglandaceae and Betulaceae 

 wherein it is the chief acid in all eight genera tested. The former 

 family is usually placed alone in the order Juglandales while the lat- 

 ter family is included with the Fagaceae in the order Fagales. Since 

 citrulline is absent in the three genera of the Fagaceae tested, the dis- 

 tribution of this compound (as a principal amino acid) is significant. 



CH2NHCNH2 

 CH2 II 

 CH2 

 CHNH2 

 COOH 



citrulline 



A third acid, 6-acetylornithine, is probably the outstanding 

 example cited by Renter since it is restricted in the Papaverales to 

 the sub-family Fumarioideae of the Papaveraceae where it was found 

 to be present as the chief amino acid among all of the nineteen 

 species (representing four genera) examined. It was not found 

 as a principal amino acid in any of fifteen genera of the sub-family 

 Papaveroideae tested although a small amount is present in Hylome- 

 con, Chelidonium majus, and Glaucium flavum. In a later section, 

 additional biochemical data bearing on the relationship between the 

 Papaveroideae and the Fumarioideae will be presented and discussed 

 (Chapter 9). 5-Acetylornithine also occurs in ferns (Asplenium) and 

 grasses. Unusual amino acids which occur in widely separated taxa 

 provide potential opportunities to study analogous enzymes or anal- 

 ogous biosynthetic routes as defined in a previous chapter, but 

 they are not likely to have any direct systematic use at higher taxo- 

 nomic levels. 



CH2NHCCH3 

 CH2 II 

 CH2 

 CHNH2 

 COOH 



d-acetylornithine 



A fourth acid, proline, which was once considered to be some- 

 what rare, is now reported from a number of different species in the 

 Leguminosae. Additional genera of other families, which have a high 

 proline concentration, are Taraxacum (Compositae), Mahonia (Ber- 

 beridaceae), Eleagnus (Eleagnaceae), Tamarix (Tamaricaceae), Phello- 

 dendron (Rutaceae), Ailanthus (Simarubaceae), and Moras (Mora- 

 ceae). 



