Theanine production by coupled fermentation with energy transfer employing Pseudomonas taetrolens Y-30 glutamine synthetase and baker's yeast cells

Abstract

Theanine was formed from glutamic acid and ethylamine by coupling the reaction of glutamine synthetase (GS) of Pseudomonas taetrolens Y-30 with sugar fermentation of baker's yeast cells as an ATP-regeneration system. Theanine formation was stimulated by the addition of Mn2+ to the mixture for the coupling. The addition of Mg2+ was less effective. In a mixture containing a larger amount of yeast cells with a fixed level of GS, glucose (the energy source) was consumed rapidly, resulting in a decrease in the final yield of theanine. On the other hand, an increase in GS amounts increased theanine formation in a mixture with a fixed amount of yeast cells. High concentrations of ethylamine enhanced theanine formation whereas inhibited yeast fermentation of sugar and the two contrary effects of ethylamine caused a high yield of theanine based on glucose consumed. In an improved reaction mixture containing 200 mM sodium glutamate, 1,200 mM ethylamine, 300 mM glucose, 50 mM potassium phosphate buffer (pH 7.0), 5 mM MnCl2, 5 mM AMP, 100 units/ml GS, and 60 mg/ml yeast cells, approximately 170 mM theanine was formed in 48 h.