Y-glutamyl amino acid

Glutathione + amino acid —> y-glutamyl-amino acid + cysteinylglycine... 

It is known that peptides and proteins exhibit a higher absorbance at wavelengths below 240 nm than the component amino acids (40, 41) and that the absorbance at 205 nm of peptides and proteins is approximately proportional to the number of peptide bonds. Pyrrolidone carboxylic acid, which has an internal peptide bond, exhibits this type of absorbance, which may be used under appropriate conditions for its quantitative determination. Thus, Orlowski et al. (13) followed the activity of y-glutamyl cyclotransferase by this procedure after incubation of the enzyme with y-glutamyl amino acids, the reaction mixture was passed through a small column of Dowex 50 (H+) in order to remove interfering substances, and the absorbance of the eluate at 205 nm was then determined. 

VII. Enzymic Formation of Pyrrolidone Carboxylic Add from y-Glutamyl Amino Acids... 

The amino acid substrates that are most recognized by Y-glulamyltranspeplidase are cysteine, glutamine, methioniney alanine, and serine. The products of the reaction, apparently, are efficiently transported into the epithelial cell, and then broken down into their constituent amino acids in the cell. The elucidation of the series of reactions involving formation of the y-glutamyl-amino acid, absorption of the products, hydrolysis of the products, and ro-formation of glutathione was mainly the work of Alton Meister (Meister, 1989). 

Gly + y-glutamyl amino acid. The products are transported into the cell and are cleaved, the Clys-Gly to Gly and Cys, and the y-glutamyl amino acid to 5-oxoproline and the amino acid. S-Oxoproline is converted to glutamic acid, so that the y-glutamyl cycle can repeat. [A.Meister Science 220 (1983) 472-477]... 

Furthermore, in a very detailed investigation of the amino acid content of Beta vulgaris which permitted the identification of compounds present in extremely low concentrations only one y-glutamyl amino acid, y-glutamyl-y-aminobutyric acid, was found (54). 

Table 7. pK-Values at 25° C For Amino Acids and Derivatives Related to y-Glutamyl Derivatives and EstimatedpK-Values For y-Glutamyl Amino Acids, Oi-Glutamyl Amino Acids and Dipeptides With Glutamic Acid as C-Terminal and an ol-Amino Acid as N-Terminal... 

Separation and quantitative determination of y-glutamyl-amino acids has been performed by reaction with a mixture of 2,2,3,3,3-pentafluoro-1-propanol and pentafluoropropionic anhydride followed by gas chromatography (379). 

WiLK, S., and M. Orlowski Determination of pyrrolidone carboxylate and y-glutamyl amino acids by gas chromatography. Anal. Biochem. 69, 100 (1975). 

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