Table 1.

Kinetic parameters for the CO₂ hydration reaction catalysed by the human cytosolic isozymes hCA I and II (α-class CAs) and the β-CAs from Drosophila melanogaster (DmBCA) and Anopheles gambiae (AgaCA) measured at 20 °C, pH 7.6 in 20 mM HEPES buffer (for hCA I and II) and 20 °C, pH 8.3 in 20 mM TRIS buffer (for the β-CAs), in the presence 20 mM NaClO₄ (for maintaining constant ionic strength). Inhibition data with the clinically used sulphonamide acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulphonamide) are also provided.

Enzyme	Activity level	Class	kcat (s−1)	kcat/Km (M−1× s−1)	KI (acetazolamide) (nM)
hCA Ia	Moderate	α	2.0 × 105	5.0 × 107	250
hCA IIa	Very high	α	1.4 × 106	1.5 × 108	12
DmBCAb	High	β	9.5 × 105	1.1 × 108	516
AgaCAc	Moderate	β	7.2 × 105	5.6 × 107	27.3

^aFrom ref.^20a.

^bFrom ref.⁹.

^cFrom ref.¹⁶.