1. Selective inhibition of homocysteine-induced seizures by glutamic acid diethyl ester and other glutamate esters
W J Freed Epilepsia. 1985 Jan-Feb;26(1):30-6. doi: 10.1111/j.1528-1157.1985.tb05185.x.
Homocysteine thiolactone causes convulsions when administered to animals, and has recently been reported to have excitatory effects on neurons in the central nervous system. Glutamic acid diethyl ester (GDEE) has previously been found to be an effective antagonist of the central excitation induced by homocysteine and is thought to be a selective antagonist of the quisqualate-sensitive excitatory amino-acid-receptor site. If an interaction of homocysteine with the quisqualate-sensitive receptor site is responsible for its convulsive properties, GDEE might also block the induction of seizures by homocysteine. GDEE in a dosage of 4 mmol/kg almost completely blocked homocysteine-induced seizures in mice; smaller dosages had no effect or only slight inhibitory effects. Glutamic acid dimethyl ester (GDME) and glutamic acid gamma-methyl ester (GMME) also partially blocked homocysteine-induced seizures, but monosodium glutamate and glutamic acid gamma-monoethyl ester (GMEE) had only a slight effect. None of the glutamate esters inhibited seizures induced by pentylenetetrazole. It is therefore suggested that certain types of seizures involve the quisqualic acid excitatory amino-acid-receptor site. Homocysteine-induced seizures may serve as a model of seizures of this type, and GDEE, GDME, and GMME may be effective antagonists of such seizures.
2. Enzymatic synthesis of γ-glutamylmethylamide from glutamic acid γ-methyl ester and methylamine catalyzed by Escherichia coli having γ-glutamyltranspeptidase activity
Lisheng Xu, Guizhen Gao, Cao Wengen, Jigui Xu, Liang Zhao, Hongwei Shi, Xingtao Zhang Appl Biochem Biotechnol. 2014 Jun;173(4):851-6. doi: 10.1007/s12010-014-0877-3. Epub 2014 Apr 15.
A new method for the synthesis of γ-glutamylmethylamide is presented. Glutamic acid γ-methyl ester was used as substrate for γ-glutamylmethylamide synthesis catalyzed by Escherichia coli with γ-glutamyltranspeptidase activity. Reaction conditions were optimized by using 300 mM glutamic acid γ-methyl ester and 3,000 mM methylamine at pH 10 and 40 °C. Bioconversion rate of γ-glutamylmethylamide reached 87 % after 10 h. γ-Glutamyltranspeptidase was reversibly inhibited only when glutamic acid γ-methyl ester was above 300 mM.
3. Enzymatic synthesis of theanine from glutamic acid γ-methyl ester and ethylamine by immobilized Escherichia coli cells with γ-glutamyltranspeptidase activity
Fei Zhang, Qing-Zhong Zheng, Qing-Cai Jiao, Jun-Zhong Liu, Gen-Hai Zhao Amino Acids. 2010 Nov;39(5):1177-82. doi: 10.1007/s00726-010-0553-z. Epub 2010 Mar 19.
Theanine (γ-glutamylethylamide) is the main amino acid component in green tea. The demand for theanine in the food and pharmaceutical industries continues to increase because of its special flavour and multiple physiological effects. In this research, an improved method for enzymatic theanine synthesis is reported. An economical substrate, glutamic acid γ-methyl ester, was used in the synthesis catalyzed by immobilized Escherichia coli cells with γ-glutamyltranspeptidase (GGT) activity. The results show that GGT activity with glutamic acid γ-methyl ester as substrate was about 1.2-folds higher than that with glutamine as substrate. Reaction conditions were optimized by using 300 mmol/l glutamic acid γ-methyl ester, 3,000 mmol/l ethylamine, and 0.1 g/ml of immobilized GGT cells at pH 10 and 50°C. Under these conditions, the immobilized cells were continuously used ten times, yielding an average glutamic acid γ-methyl ester to theanine conversion rate of 69.3%. Bead activity did not change significantly the first six times they were used, and the average conversion rate during the first six instances was 87.2%. The immobilized cells exhibited favourable operational stability.