Synthesis of y-glutamyl-L-3,4-dihydroxyphenylalanine from a y-glutamyl donor (glutathione or glutamine) and DOPA(L-3,4-dihydroxyphenylalanine)was examined making use of the partially purified y-glutamyltranspeptidase from a bacterium, Proteus mirabilis.The optimum pH for yglutamyl-DOPA synthesis from glutathione was 9.5 to 1 1 and the amount of peptide produced increased with the glutathione concentration.The best conditions for y-glutamyl-DOPA synthesis were investigated and 13mg/ml of y-glutamyl-DOPA was synthesized with a yield of 6.7% of the substrate, glutathione.The product was isolated from a large scale reaction mixture and the structure determined by physicochemical analyses; PMRspectrometry, mass spectrometry and IR spectrometry.y-Glutamyl-DOPA synthesis was also performed with glutamine as the y-glutamyl donor.y-Glutamyltranspeptidase (EC 2.3.2.2) (y-GT) catalyzes the hydrolysis of glutathione and the transfer of the y-glutamyl moiety to a large variety of amino acids and peptides.1<2)y-Glu-Cys-Gly + H2O >Glu+Cys-Gly y-Glu-Cys-Gly +A(P) > }'-Glu-A(P)+Cys-Gly (A, amino acids; P, peptides)
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Nakayama et al. (1985) studied this question.