1. Figure S1; ATase removal KG=1.0 mM Transient response to a sudden increase in the ammonium availability from 0.05 to 1.0 mM and removal of ATase at time zero. The -ketoglutarate concentration was 1.0 mM. A: rates of glutamine synthetase (v GS ), glutamate synthase (v GOGAT ) and glutamate dehydrogenase (v GDH ). B: adenylylation state of glutamine synthetase (n AMP ) and the 'apparent' maximal rate of glutamine synthetase. C: concentrations of glutamine (GLN), PII with one 2-ketoglutarate attached to it (PIIKG 1 ), and PII saturated with UMP and -ketoglutarate (PIIUMP 3 KG 3 ). A. B. C.

2. Figure S2; UTase removal KG=1.0 mM Transient response to a sudden increase in the ammonium availability from 0.05 to 1.0 mM and removal of UTase at time zero. The -ketoglutarate concentration was 1.0 mM. A: rates of glutamine synthetase (v GS ), glutamate synthase (v GOGAT ) and glutamate dehydrogenase (v GDH ). B: adenylylation state of glutamine synthetase (n AMP ) and the 'apparent' maximal rate of glutamine synthetase. C: concentrations of glutamine (GLN), PII with one 2-ketoglutarate attached to it (PIIKG 1 ), and PII saturated with UMP and -ketoglutarate (PIIUMP 3 KG 3 ). A. B. C.

3. Figure S3; PII removal KG=1.0 mM Transient response to a sudden increase in the ammonium availability from 0.05 to 1.0 mM and removal of PII at time zero. The -ketoglutarate concentration was 1.0 mM. A: rates of glutamine synthetase (v GS ), glutamate synthase (v GOGAT ) and glutamate dehydrogenase (v GDH ). B: adenylylation state of glutamine synthetase (n AMP ) and the 'apparent' maximal rate of glutamine synthetase. C: concentrations of glutamine (GLN), PII with one -ketoglutarate attached to it (PIIKG 1 ), and PII saturated with UMP and -ketoglutarate (PIIUMP 3 KG 3 ). A. B. C.

4. Figure S4; transient regulatory contributions The transient regulatory contributions of the regulators of GS are displayed upon a sudden increase in the ammonium concentrations at time zero (Fig. 3). On the left the calculations were performed at 0.2 mM KG and on the right at 1.0 mM KG. The values for ADP have been divided by 10.

5. Figure S5; J N as function of the maximal rates of GS and GOGAT Ammonium assimilation flux as function the maximal rates of GS and GOGAT at conditions of ammonium-limited chemostat (NH4+=0.05 mM, KG=0.2 mM, V GDH =360 mM/min). The dot resembles the conditions of the kinetic model used in previous calculations (Table 3A; 3 rd row, 12 th column).