Conversion of Glutamic Acid to γ -Aminobutyric Acid in Tea Leaves under Anaerobic Conditions

γ-Aminobutyric acid (GABA), a hypotensive compound, and alanine accumulated in tea leaves under anaerobic conditions. Since the 15N in 15N-glutamic acid was well incorporated in GABA and alanine during anaerobic incubation, glutamic acid seemed to be a source of nitrogen for the increased GABA and alanine. GOT and GPT were the predominant amino acid transaminases in tea leaves. Although glutamate decarboxylase and GPT seemed to be important for GABA and alanine accumulation, the activities of these enzymes did not increase under anaerobic conditions. Glutamate decarboxylase, which formed GABA from glutamate, was purified 52.4-fold. This enzyme, with an optimum pH at 5.8, was activated by pyridoxal phosphate and used only l-glutamic acid as a substrate.