gamma-Glu-Cys (γ-Glu-Cys) is a substrate for biosynthesis of L-glutathione by glutathione synthetase. γ-Glu-Cys is produced by cleaving the Cys-Gly peptide bond of glutathione. It is also necessary for the formation of phytochelins, which are cysteine-rich thiol-reactive peptides[1].
Reference:
[1]. Anjum N A, Gill S S, Gill R, et al. Plant adaptation to environmental change: significance of amino acids and their derivatives. 2014.