Table 1.

Structural and enzymatic characteristics of synthase–glutaminase complexes comprising either the stTrpEx_Δ synthase or the ppPabA* glutaminase

		Kinetic parameters of AS formation‡			Glutaminase activity§
Synthase–glutaminase pairs	Complex formation,† native MS	kcat, s−1	KmCH, μM	kcat/KmCH, M−1⋅s−1	fstim
stTrpEx_Δ + stTrpG	Ex_Δ2:G2 tetramer	—	—	—	n.a.
stTrpEx_Δ + ecTrpGD	Ex_Δ2:GD2 tetramer	—	—	—	n.a.
stTrpEx_Δ + ppPabA	Ex_Δ2:A2 tetramer	—	—	—	2.0 ± 0.1
stTrpEx_Δ + smPabA	Ex_Δ2:A2 tetramer	—	—	—	<2.0
stTrpEx_Δ + ecPabA	Ex_Δ2:A2 tetramer	—	—	—	<2.0
stTrpEx_Δ + bsPabA	Ex_Δ2:A2 tetramer	—	—	—	<2.0
ppPabA* + stTrpEx	Ex2:A2 tetramer	0.31 ± 0.05	6.2 ± 3.5	5.6 × 104	41.8 ± 3.0
ppPabA* + ecTrpEx	Ex2:A2 tetramer	0.63 ± 0.05	9.6 ± 2.0	6.7 × 104	45.2 ± 3.3
ppPabA* + smTrpEx	Ex2:A2 tetramer	0.04 ± 0.004	5.2 ± 2.8	8.8 × 103	49.0 ± 2.7
ppPabA* + ppTrpE	E2:A2 tetramer	0.9 ± 0.06	8.4 ± 1.8	1.1 × 105	11.5 ± 3.0
ppPabA* + ppPabB	B:A dimer	0.2 ± 0.03	25.0 ± 2.6	6.7 × 103	19.1 ± 0.6

^†Representative spectra and molecular weights are provided in SI Appendix, Fig. S8 and Table S7.

^‡Values are the mean and SD from at least three independent measurements. stTrpEx_Δ was inactive (−).

^§Stimulation factors (f_stim) are based on the apparent glutamine hydrolysis rate of the listed glutaminases (SI Appendix, Table S9) and that of ppPabA* (k_app = 0.005 s⁻¹). Glutaminase stimulation at the lower end of the assay detection limit is <2.0. n.a., not applicable (TrpG glutaminases do not display glutaminase activity in the absence of a synthase).