Glutamine synthetase (GS), encoded by the GLUL gene, is a key enzyme in nitrogen metabolism that catalyzes the ATP-dependent conversion of glutamate and ammonia into glutamine. Widely expressed in tissues like the liver, brain, and kidneys, it maintains nitrogen homeostasis—detoxifying ammonia in the liver and supporting neurotransmitter synthesis in the brain. GS also plays a critical role in cancer metabolism, as rapidly dividing tumor cells rely on glutamine for energy and biosynthesis. GS and GLS (glutaminase) function in a cyclic relationship: GLS breaks down glutamine into glutamate, which GS then uses to resynthesize glutamine, though they do not directly bind physically.To detect the activity of recombinant GS , a functional ELISA assay was performed to evaluate the interaction between recombinant human GS and recombinant human GLS.Briefly, GLS was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to GS-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-GLS pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450/630nm immediately.Measured by its binding ability in a functional ELISA. When Recombinant GS is lmmobilized at 2 µg/mL(100 uLwell), the concentration of GLS that produces 50% optimal bindingresponse is found to be approximately 0.00494 µg/mL.