Probably involved in nitrogen metabolism via ammonium assimilation. Catalyzes the ATP-dependent biosynthesis of glutamine from glutamate and ammonia. ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Binds 2 Mg(2+) ions per subunit. Directly stimulated by the effector molecule 2-oxoglutarate. Inhibited by GlnK1. 2-oxoglutarate antagonizes the inhibitory effects of GlnK1, but does not prevent GlnK1/GlnA1 complex formation. Homohexamer. Interacts and forms stable complexes with the regulatory protein GlnK1. Belongs to the glutamine synthetase family.