TABLE 2.

Kinetic constants for the D. radiodurans thioredoxin system using both D. radiodurans Trx1 and E. coli Trx1 as substrates^a

Assay	Km (μM)	kcat (s−1)	kcat/Km (M−1 s−1)
D. radiodurans TrxR/D. radiodurans Trx1	5.7 ± 1.9 (2.75 ± 0.40)	1.1 ± 0.1 (9.4 ± 1.0)	1.9 × 105 (3.4 × 106)
D. radiodurans TrxR/E. coli Trx1	32.4 ± 8.5	18.0 ± 2.6	5.5 × 105
E. coli TrxR/D. radiodurans Trx1	44.4 ± 5.5	4.6 ± 0.2	1.0 × 105
E. coli TrxR/E. coli Trx1	2.7 ± 0.7 (0.7 ± 0.003)	3.6 ± 0.01 (4.4 ± 0.04)	1.3 × 106 (6.3 × 106)

^aThe k_cat values for the E. coli system clones are about sixfold lower than the literature values, using both the insulin reduction and DTNB reduction assays (in parentheses) (15, 24).