Table 1.
Activation of human carbonic anhydrase (hCA) isozymes I, II, and EhiCA with L-Trp at 25 °C for the CO2 hydration reaction [38].
| Isozyme | kcat * | KM * | (kcat)L-Trp ** | KA *** (µM) |
|---|---|---|---|---|
| (s−1) | (mM) | (s−1) | 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 |
| LdCA | 9.35 × 105 | 15.8 | 1.9 × 106 | 4.02 |
| EhiCA b | 6.7 × 105 | 7.5 | 1.9 × 106 | 5.24 |
* Observed catalytic rate without activator. KM values in the presence and the absence of activators were the same for the various CAs (data not shown).; ** Observed catalytic rate in the presence of 10 µM activator; *** The activation constant (KA) for each enzyme was obtained by fitting the observed catalytic enhancements as a function of the activator concentration [41]. Mean from at least three determinations by a stopped-flow, CO2 hydrase method [38]. Standard errors were in the range of 5–10% of the reported values (data not shown); a Human recombinant isozymes, from ref. [32]; b Protozoan recombinant enzyme, this work.