Table 3. Growth characteristics of EcAmtB and ScMep2 variants.

Amt phenotype	Growth rate (OD600/hr)
	Glutamate	NH4Cl
S. cerevisae wild-type	0.175±0.005	0.150±0.007
S. cerevisae Δmep	0.175±0.007	0.015±0.004
EcAmtB wild-type	0.120±0.006	0.080±0.005
EcAmtB H168A	0.145±0.008	0.080±0.007
EcAmtB H318A	0.148±0.008	0.060±0.019
EcAmtB H168A/H318A	0.145±0.010	0.015±0.001
EcAmtB F215A	0.140±0.008	0.010±0.001
ScMep2 wild-type	0.135±0.005	0.115±0.007
ScMep2 H194A	0.165±0.012	0.090±0.005
ScMep2 H348A	0.145±0.014	0.100±0.010
ScMep2 H194A/H348A	0.135±0.010	0.015±0.002

S. cerevisae strains were grown in YNB liquid medium pH 6.0 with either 30 mM glutamate or 3 mM NH₄Cl as the sole nitrogen source. The growth rate in logarithmic phase was recorded as OD₆₀₀/hr and the data are the means of six replicate experiments. Wild-type S. cerevisae (strain 23344c) and S. cerevisae Δmep strain (31019b) were used as controls. EcAmtB and ScMep2 variants were all expressed in S. cerevisae Δmep strain (31019b).