58 J. F. THOMPSON et al. 
Concluding comments. The above discussion of y-glutamyl compounds is summarized 
in Table I. Of the 19 compounds listed, adequate proof of structure is available for 
16. The non-glutamyl portion is a protein amino acid in five cases and is a non-protein 
amino acid in three. 
Dipeptides have been isolated mainly from storage tissues such as seeds and bulbs 
but also have been obtained from other tissues. Fungi, monocotyledons and dicotyle- 
dons were sources of isolated compounds. These facts indicate the possibility that 
glutamyl dipeptides may have widespread occurrence in various types of tissues 
throughout the plant kingdom. 
QUANTITY OF PEPTIDES IN PLANTS 
The content of several peptides and related compounds in certain plant tissues is 
presented in Table II. These data reveal several interesting points. The dipeptides 
make an appreciable contribution to the total non-protein amino nitrogen fraction. 
For example, y-glutamyl-S-methylcysteine accounts for over 40%, of the free amino 
nitrogen in kidney beans. At the same time the content of glutamic acid is less than 
10%, and that of methylcysteine is far less than this. 
Even though glutamic acid is usually a prominent constituent of the non-protein 
fraction of plants, the y-glutamyl peptides often are present in concentrations as high 
or higher than that of glutamic acid. The situation is even more striking with respect 
to the non-glutamic acid moiety of the peptides where the molar ratio of peptide- 
form to free form may be in the order of roo or 1000 : t (Table IT). 
The data in Table II indicate amounts of peptides in tissues from which they were 
TABLE II 
THE QUANTITY OF Yy-GLUTAMYL PEPTIDES AND RELATED COMPOUNDS IN PLANT TISSUE 

Content* 
pumoles| Mole ratio 
Compound Tissue Lg/g roo atoms peptide 
fresh wt. non-protein free form 
nitrogen** 
y-Glutamyl-S-methylcysteine Kidney bean seed 4600 42.6 
Glutamic acid Kidney bean seed 400 6.6 6.45 
S-Methylcysteine Kidney bean seed 221 3.2 13.3 
y-Glutamyl-$-amino- Iris bulb 632 15.8 
isobutyric acid 
y-Glutamyl-$-alanine Iris bulb 97 2.6 
Glutamic acid Iris bulb 452 17.8 1.03 
f-Aminoisobutyric acid Iris bulb 2.00 0.01 1580 
f-Alanine Iris bulb 0.90 0.005 520 
Glutathione Iris bulb 138 2.57 
y-Glutamyltyrosine Soy bean seed 384 4-94 
y-Glutamylphenylalanine Soy bean seed 393 4.66 
Glutamic acid Soy bean seed 636 L723 0.55 
Tyrosine Soy bean seed MeSer7, 0.18 27-5 
Phenylalanine Soy bean seed Gy) 0.70 6.7 
* Data on kidney bean and soy bean seeds was obtained by quantitative paper chromatography”?, 
after purification on resins®: *. Data from iris bulb was obtained by the method of Moore et al.*4 5, 
** Nitrogen determined by reaction with ninhydrin after removal of ammonia®*. 
References p. 64 
