Table 1.

Activation of hCA isozymes I, II and BsuCA 1/FtuCA, with L-Trp, at 25 °C, for the CO₂ hydration reaction ²⁰ .

Isozyme	kcat (s−1) a	KM (mM) a	(kcat)L-Trp (s−1) b	KA (μM) L-Trp c
hCA I d	2.0 × 105	4.0	3.4 × 105	44
hCA II d	1.4 × 106	9.3	4.9 × 106	27
BsuCA 1 e	6.4 × 105	16.4	25.9 × 105	1.25
FtuCA e	9.8 × 105	11.0	15.7 × 105	34.1

^aObserved catalytic rate without activator. K _M values in the presence and the absence of activators were the same for the various CAs (data not shown).

^bObserved catalytic rate in the presence of 10 μM activator.

^cThe activation constant (K _A) for each enzyme was obtained by fitting the observed catalytic enhancements as a function of the activator concentration ^21–29 . Mean from at least three determinations by a stopped-flow, CO₂ hydrase method ²⁰ . Standard errors were in the range of 5–10% of the reported values (data not shown).

^dHuman recombinant isozymes, from Supuran ⁸ a.

^eBacterial recombinant enzyme, this work.