SOLUBLE, NITROGENOUS CONSTITUENTS OF PLANTS 29 
y-Aminobutyric acid (y-A B) 
Long known as a bacterial by product, y-aminobutyric acid was first detected (DENT, 
STEPKA AND STEWARD?®, cf. Fig. 1) and later proved (THoMPSON, POLLARD AND STE- 
WARD**) to be prominent in higher plants from work done initially on the potato tuber, 
where it is one of the most prominent compounds in the soluble nitrogen fraction. The 
compound soon appeared to be ubiquitous in the plant kingdom and was one of the first 
non-a-amino, non-protein amino acids to be conspicuous. Although structurally related 
to glutamic acid, as if by decarboxylation of the a-COOH, it now appears that it is not 
formed in this way in carrot cultures, for it readily gives rise to glutamic acid, or rather 
to glutamine, whereas glutamine (or glutamic acid) supplied exogenously does not easily 
form y-AB in vivo (STEWARD, BIDWELL AND YEMM?"). It is now believed that y-AB 
originates from a nitrogen-free “port of entry”, probably succinic semi-aldehyde and 
that its nitrogen may be incorporated eventually in protein, though not of course as 
y-AB which has never been demonstrated to be a protein constituent. Thus a com- 
pound first noticed in higher plants as a spot on a chromatogram in 1947 is now rec- 
ognized as a well authenticated and widespread plant product with unexpected 
metabolic implications, and it has also received very active consideration in the 
metabolism of brain and other tissues (ROBERTS AND BREGOFF24; BAXTER AND 
Roperts*). The range of possible or demonstrable reactions involving y-AB were 
summarized by the authors (1956), and since then the presumed reactions through 
succinic acid and its semi-aldehyde to y-AB have been substantiated by enzymatic 
studies (BACHRACH!). 
PHASEOLUS VULGARIS = ALC. SOL. N. COMPOS. OF PEDICELS 
VALINE 
-— 
re 3 
© 
BY - Aminosutyric 

O-AwINOADIPIC 
GLUTAMIC 
rg | ASPARTIC 

BUTANOL = ACETIC ——> 

UNKNOWN XK 
4— PHENOL 
Fig. 3. Chromatogram to show the presence of a-aminoadipic acid, which became radioactive when 
4C-lysine was supplied. 
References p. 42 
