TABLE 3.
Apparent steady-state kinetic parameters of ISPs for selected substituted benzoatesa
| ISP | Substrate | KmA (μM) | KmO2 μM | kcat (s−1) | kcat/KmA (104 M−1 s−1) | kcat/KmO2 (104 M−1 s−1) |
|---|---|---|---|---|---|---|
| αBβB | Benzoate | 26 (1) | 53 (2) | 8.6 (0.1) | 33 (3) | 16 (1) |
| 2-Methylbenzoate | 1,401 (48) | 247 (20) | 4.2 (0.2) | 0.3 (0.1) | 1.7 (0.9) | |
| 3-Methylbenzoate | 89 (6) | 129 (11) | 7.0 (0.5) | 8 (2) | 5.4 (0.4) | |
| 3-Chlorobenzoate | 113 (8) | 128 (11) | 3.0 (0.1) | 3 (1) | 2.3 (0.5) | |
| αTβTc | Benzoate | 19 (4) | 13 (2) | 2.8 (0.1) | 15 (3) | 22 (2) |
| 2-Methylbenzoate | 250 (65) | 46 (10) | 2.3 (0.13)b | 0.9 (0.2)b | 4.9 (0.9) | |
| 3-Methylbenzoate | 9.1 (1.3) | 16 (2) | 3.9 (0.2) | 43 (4) | 25 (2) | |
| 4-Methylbenzoate | 28 (6) | 8.4 (1.5) | 2.5 (0.1) | 9 (2) | 30 (4) | |
| 2-Chlorobenzoate | 144 (90) | 92 (22) | 1.9 (0.1)b | 13 (0.8)b | 2.1 (0.4) | |
| 3-Chlorobenzoate | 26 (3) | 19 (6) | 3.1 (0.1) | 15 (1) | 21 (1) | |
| 4-Chlorobenzoate | 41 (9) | 12 (2) | 3.0 (0.1) | 8 (1) | 25 (3) |
a
Experiments were performed with 0.1 M sodium phosphate (pH 7.0 at 25°C) containing 430 μM NADH. Standard errors are given in parentheses. ht-REDs were paired with the α subunit of the ISP. The data sets used to calculate the parameters for different substrates contain 80 to 110 points. BADO displayed no detectable activity in the presence of either 4-methylbenzoate, 2-chlorobenzoate, or 4-chlorobenzoate.
b
Values were based on O2 consumption to be consistent with the other values in the table. Values calculated based on benzoate consumption were at least one order of magnitude lower.
c
Values published in reference 20.