62 J. F. THOMPSON et al. 
TABLE VI 
EVIDENCE FOR TRANSPEPTIDASE AND A Y-GLUTAMYL BOND PEPTIDASE ACTIVITY 
IN BEAN SEED PREPARATIONS 
mmoles of aniline** 
Fraction* Additions liberated beyond 
zero-time control 


o-30°%, saturation None 10.7 
Ammonium sulfate L-Methionine 16.1 
S-Methyl-L-cysteine 16.6 
30-40% saturation None 13.0 
Ammonium sulfate L-Methionine 16.5 
S-Methyl-L-cysteine 16.7 


* Bean seed extract was prepared by grinding 25 g of dry kidney bean seeds with 
50 ml of 0.o40 M NaHCO3. 
** The reaction mixture contained 0.5 ml of bean extract with these additions (in 
moles) :y-glutamylaniline, 1.12; Tris buffer (pH 8.6), 50; aminoacids, 5.62; toa total 
volume of 1.5 ml. Incubation was for 2 h at 25°. Aniline was determined by diazo- 
tization and coupling with /-naphthylethylenediamine". 
sequent dialysis should have removed free amino acids. The additional release of 
aniline as a result of the addition of methionine or methylcysteine provides some 
evidence of the presence of a transpeptidase. Due to the considerable difference in the 
ratio of peptidase to transpeptidase activity in the two ammonium sulfate fractions 
(Table VI), it appears that these results are not explained by a hydrolysis or an amino- 
lysis induced only by a transpeptidase*’. The peptide-bond cleavage induced by bean 
extracts is consistent with the loss of y-glutamylmethylcysteine in germinating 
kidney bean seeds (Table IV). 
DISCUSSION: POSSIBLE PHYSIOLOGICAL ROLE OF y-GLUTAMYL COMPOUNDS 
Because y-glutamyl compounds are numerous (Table I), occur in relatively high 
concentrations in some tissues (Table II) and exist in diverse plants and tissues 
(Tables I-III), it is not unreasonable to assume that they play a role in normal plant 
metabolism. All of these compounds are closely related chemically and may be formed 
in a similar manner. 
Transpeptidases have been extensively studied in animal extracts but not in plant 
extracts although dipeptides have been found in plants but not in animals®®. Although 
the role of transpeptidation in normal metabolism has not been elucidated, with the 
discovery of y-glutamyl peptides in plants, a possible function for transpeptidases 
can be visualized. In plants they may be involved in formation of dipeptides while in 
animals they may act to help hydrolyze dipeptides that are in the diet. The glutamino- 
transferases? of animals and higher plants transfer y-glutamyl groups to amines but 
not amino acids and hence are not involved in y-glutamyl] peptide metabolism. Certain 
bacterial enzyme preparations do transfer y-glutamyl groups to amines and to amino 
acids but the only amino acid acceptor is glutamic acid*: 43, 
References p. 64 
