. 2013 Oct 24;288(50):35801–35811. doi: 10.1074/jbc.M113.519496

TABLE 4.

Glutamine synthetase cooperativity assay

Enzyme	Glutamine synthetase-specific activity
	Forward reaction (biosynthetic)		Reverse reaction (transferase)^a
	Mg²⁺-dependent^a	Mn²⁺-dependent^a	Reverse reaction (transferase)^a
WT	0.406 ± 0.035	0.187 ± 0.009	9.555 ± 0.490
WT (treated)^b	0.413 ± 0.019	0.193 ± 0.012	9.643 ± 0.422
GS(E304A/A305G)	0.003 ± 0.001	0.005 ± 0.004	0.029 ± 0.007
GS(E304A/A305G) (treated)^b	0.003 ± 0.001	0.005 ± 0.002	0.038 ± 0.014
WT-E304A/A305G mixed complex	0.005 ± 0.001	0.006 ± 0.004	0.037 ± 0.012

^a 1 unit of GS activity corresponds to the ATP/ADP-dependent formation of 1 nmol of γ-glutamylhydroxamate min⁻¹.

^b Samples were treated with 2 m urea then dialyzed to remove urea (see “Experimental Procedures”).