Table 1. Activities of Arabidopsis and E. coli ADC synthases with various amino donors.

	Enzyme activity, nmol·h-1·mg-1 protein
Amino donor	AtADCS	PabA + PabB
l-Glutamine 5 mM	4.0 ± 0.3	35.0 ± 3.0
l-Asparagine 5 mM	<0.01	<0.01
[NH4+ + NH3] 52 mM	2.0 ± 0.2	2.8 ± 0.4

Assay conditions were based on those developed for the E. coli enzyme (19), as described in Materials and Methods. All assays contained excess PabC to convert ADC to PABA, which was determined by HPLC fluorescence. The AtADCS preparation was partially purified by size exclusion chromatography (Fig. 4A). E. coli PabA and PabB preparations were desalted extracts of cells overexpressing each protein. Data are means ± SE of five replicates.