Table 1. Metal Content and Reactivity of Different AibH1H2 Preparations^a.

	metal/heterodimer
	Fe	Mn	Ni	Zn	[d-MeSer]/[AibH1H2]b
FeAibH1H2	2.8 ± 0.1	0.08 ± 0.04	0.03 ± 0.03	0c	<2d
LBAibH1H2	1.67 ± 0.07	1.05 ± 0.01	0.055 ± 0.003	0.131 ± 0.004	33 ± 1
MnAibH1H2	0.4 ± 0.1	2.2 ± 0.4	0.03 ± 0.07	0	110 ± 30
Mn*AibH1H2	0	2.4 ± 0.3	0	0	50 ± 10
Fe*AibH1 H2	1.8 ± 0.2	0	0	0	<2
Mn/Fe Crystal	0.0	1.9	1.3e	0.0	30
EPR	0.3	1.5	0.0	0.1	73

^aData for entries 1–5 represent the average of at least three technical replicates. Error is the standard deviation. Entries 6 and 7 represent the specific batch used for the application indicated. Error of the ICP-OES instrument is less than 0.01 ppm.

^bCatalytic activity assay performed with the addition of one equivalent of Fe^II relative to AibH1H2 (25 μM) in the reaction mixture.

^cValues less than the limit of detection of the ICP-OES instrument (0.01 ppm) are reported as zero.

^dValues less than 2 are below the minimum point on the calibration curve for GC-MS analysis of catalytic activity.

^eHigh Ni content is likely due to contamination from the Ni-NTA column during protein purification.