Table 1.
Activation of human carbonic anhydrase (hCA) isozymes I, II, PhaCA and CpsCA with l-Trp, at 25 °C, for the CO2 hydration reaction [42].
| Isozyme | kcat 1 (s−1) | KM 1 (mM) | (kcat) l-Trp 2 (s−1) | KA 3 (μM) l-Trp |
|---|---|---|---|---|
| hCA I a | 2.0 × 105 | 4.0 | 3.4 × 105 | 44.0 |
| hCA II a | 1.4 × 106 | 9.3 | 4.9 × 106 | 27.0 |
| PhaCA b | 1.4 × 105 | 7.3 | 7.6 × 105 | 7.12 |
| CpsCA b | 6.0 × 105 | 12.7 | 9.9 × 105 | 21.3 |
1 Observed catalytic rate without activator. KM values in the presence and the absence of activators were the same for the various carbonic anhydrases (CAs) (data not shown). 2 Observed catalytic rate in the presence of 10 μM activator. 3 The activation constant (KA) for each enzyme was obtained by fitting the observed catalytic enhancements as a function of the activator concentration [41]. The mean was obtained from at least three determinations by a stopped-flow CO2 hydrase method [42]. Standard errors were in the range of 5–10% of the reported values (data not shown). a Human recombinant isozymes, from [32]; b Antarctic bacteria recombinant enzyme, this work.