Glutamyl peptides

L-7-Glutamyl-peptide + amino acid peptide + i.-glutamyl-amino acid... 

Since that time a very considerable number of small peptides containing 7-glutamyl linkages have been reported. Some of those found very recently are included in Table III, together with those mentioned above. The recent papers refer to some naturally occurring 7-glutamyl peptides which had been found previously, and these are also reported by Wald-schmidt-Leitz and Reicheneder (1961), and Franzblau (1962). 

In all the 7-glutamyl peptides reported glutamic acid residues linked via the 7-carboxyl groups have the a-carboxyl free and therefore do not constitute branching points or cross-links. 

Very recently, Rojkind has isolated 7-glutamyl peptides from a col-lagenase digest of ichthyocol (see Gallop, 1964). 

Kristensen, I., and P. O. Larsen Differentiation between a-glutamyl peptides, 7-glutamyl peptides, and a-aminoacylglutamic acids by PMR spectroscopy. Acta Chem. Scand. 27, 3123 (1973). 

I don t know of any published results concerning 7-glutamyl peptides with one more peptide linkage at the amino group of the glutamic moiety. However, there is strong support that those types of compounds may also be easily hydrolyzed, although there is no possibility here to form any... 

The possible role of the 7-glutamyl peptides in transfer reactions presents an interesting puzzle at the present time. Since only the a-carboxyl... 

My ne. t comments are concerned with the function of the enzymes responsible for the hydrolysis of GSH. We have felt from the start of our work in 1946 that the hydrolysis of GSH is concerned with absorption mechanisms and onlj" indirectly with the synthesis of protein. Thus, we would explain the transpeptidation reactions f rom GSH as a mechanism of transfer of amino acids across cellular membranes. The formation of 7-glutamyl peptides would provide the concentration differential necessary for the absorption of amino acids, for e.xample, from the tubular filtrate or from the intestine. Thus, we would explain the high concentration of the enzymes responsible for transpeptidation in kidney and intestine on the basis that these tissues are the ones most concerned with absorption phenomena. 

In a similar manner there occurs the formation of 7-glutamyl peptides by sheep kidney extracts from glutathione and free amino acids. The activity of esters as substrates is shown by methionine isopropyl ester condensing to form methionylmethionine and methionylmethionylmethionine catalyzed by trypsin or by chymotrypsin. A similar condensation has been noted for threonine isopropyl ester. ... 

Headier and Greenberg (68) tested the two baae mechanisms put forward by Hanes et al., i.e., y-glutamyl activation is an important first step in peptide synthesis and the stabilization of 7-glutamyl peptide bonds by free amino acids thus facilitates amino acid incorporation into proteins. They compared the incorporation of labeled glycine in y-glutamylglycine with that of free-labeled glycine in the presence of... 

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