Overexpression and Characterization of Recombinant Glutamate Decarboxylase from Thermococcus kodakaraensis KOD1

Glutamate decarboxylase (GAD) (EC 4.1.1.15) catalyzes decarboxylation of glutamic acid to produce gamma-aminobutyric acid (GABA). A putative gad gene (tk1814) from an archaeon Thermococcus kodakaraensis KOD1 was cloned and transformed into Escherichia coli to produce a bulk amount of recombinant GAD. Activity of the purified GAD was optimal at 90℃ and pH 8.0. Optimal concentration of substrate for conversion into gamma-aminobutyric acid by recombinant GAD was 50 mM monosodium glutamate. Recombinant GAD was confirmed to be monomeric, and its activity was greatly inhibited by various salts such as sodium chloride, Tris-HCl, and sodium phosphate. K∧m, V∧max, and K∧cat values were 9.92 mM, 153.8 μmol min-¹ mg-¹, and 6.613×10³ min-¹ respectively.