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They should act almost the same on glutamate yet, one is excitatory (glutamic acid) and the other calming? (Glutamine)

Glutamine is not a neurotransmitter and is therefore not “calming” (inhibitory). It is however a precursor of glutamate (excitatory) and glutamate is a precursor of GABA (inhibitory) neurotransmitters. They act in opposition to one another, hence their tied metabolism.