Table 2.

Variants Are Defective in Catalyzing Bio-5′-AMP Synthesis^a

BirA variants	Apparent rate kapp (s−1)b	Fold decreasec
Wild type	0.136 ± 0.004	—
V214A	0.0537 ± 0.0004	2.53 ± 0.03
V219Ad	0.0064 ± 0.0003	21.25 ± 0.06
F124A	0.0218 ± 0.0004	6.24 ± 0.03
P126A	0.052 ± 0.001	2.62 ± 0.04
M211Ad	0.0043 ± 0.0003	31.63 ± 0.08
V218A	0.043 ± 0.001	3.16 ± 0.04
F124A/V218A	0.0081 ± 0.0002	16.79 ± 0.04
F124A/M211Ad	0.00072 ± 0.00002	188.88 ± 0.04

^aMeasurements were performed in Standard Buffer at 20°C as described in Materials and Methods.

^bThe apparent rates are the average of the best fit rates obtained from nonlinear least squares analysis of at least five (stopped-flow) or three (fluorimeter) traces with the standard error of the mean. Comparison of wild type with variant rates using the unpaired t-test yielded P values < 0.05. With the exception of those obtained for the wild-type protein, all transients were analyzed using the model that included a linear term for photobleaching along with the single exponential.

^cFold decrease is the rate measured for wild-type BirA divided by that measured for the variant.

^dMeasured using the fluorimeter.