y-GLUTAMYL PEPTIDES IN PLANTS 61 
peptides that were available to us (Table V). The latter peptides did not support 
growth of L.arabinosus and this agrees with the findings of WAELSCH e¢ al.°® with the 
same organism. It is desirable to extend these tests to the y-glutamyl peptides of 
cysteine, f-alanine, tyrosine and phenylalanine. L. avabinosus apparently has the 
ability to split the peptide bond between the y-carboxyl group of glutamic acid and 
cysteine but lacks this ability where the second amino acid is not cysteine. When this 
result is considered along with the evidence that in plant preparations®’ cysteine is 
the only protein amino acid which will form a y-glutamyl dipeptide from glutamic 
acid, it appears that the enzymes involved in the formation and rupture of the y- 
glutamylcysteine bond are specific for this bond. However, synthesis and breakage 
of this bond occur by different mechanisms. 
FORMATION OF V-GLUTAMYL PEPTIDES 
Because of the widespread occurrence of glutathione, its metabolism has been ex- 
tensively studied. It is obvious that the biosynthesis of the y-glutamyl dipeptides 
may be analagous to the first step of glutathione synthesis wherein y-glutamylcysteine 
is formed”. #1, The reaction for y-glutamylcysteine synthesis may be formulated as 
follows for both plants and animals: 
Synthetase 
glutamic acid + cysteine + ATP ~______ y-glutamylcysteine + ADP + Pj 
Mg?t 
This reaction is formally similar to the formation of glutamine and carnosine (/- 
alanylhistidine)#*, 4° but no evidence has been forthcoming that y-glutamyl peptides 
other than y-glutamylcysteine”® 2! are formed in an analogous fashion. We have 
made unsuccessful attempts to demonstrate the formation of y-glutamylmethyl- 
cysteine in kidney bean seedling extracts in the same way that WEBSTER obtained 
the synthesis of y-glutamylcysteine*!. 
There is much evidence available?’~** for the formation of y-glutamyl peptides 
from glutathione and free amino acids in animal tissue preparations (see above). The 
intervention of ATP is not required because there is little change in free energy. 
WILLIAMS AND THORNE®: #8 have observed an enzyme in the culture media of Bacillus 
subtilis which will form y-glutamylglutamic acid and larger poly-y-glutamyl peptides 
from glutamine. Other amino acids? not only apparently do not accept y-glutamyl 
groups but some inhibit the transfer of glutamic acid. In plants, HANEs et al.?® have 
reported a glycyl-transferring enzyme in a press juice of cabbage, and VIRTANEN AND 
BERG® suggest that y-glutamylalanine can be formed by transpeptidation in pea- 
seedling extracts. 
Utilizing the method of GOLDBARG et a.™, in which y-glutamylaniline is the sub- 
strate and the release of aniline measures breaking of the y-glutamy] bond, preliminary 
evidence has been obtained for both y-glutamyl transpeptidase and peptidase in 
kidney bean seed extracts (Table VI). In the absence of added amino acids, the 
release of aniline is presumably due to peptidase action. Although this production of 
aniline could be the result of transpeptidase action, induced by endogenous amino 
acids, this appears unlikely because the ammonium sulfate precipitation and sub- 
References p. 64 
