Anion inhibition studies of a beta carbonic anhydrase from the malaria mosquito Anopheles gambiae

Figures & data

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 I^a	Moderate	α	2.0 × 10^5	5.0 × 10^7	250
hCA II^a	Very high	α	1.4 × 10^6	1.5 × 10^8	12
DmBCA^b	High	β	9.5 × 10^5	1.1 × 10^8	516
AgaCA^c	Moderate	β	7.2 × 10^5	5.6 × 10^7	27.3

^a From ref.^20a.

^b From ref.⁹.

^c From ref.¹⁶.

Table 2. Inhibition constants of anionic inhibitors against isozymes hCA I, II (α-CA class), and DmBCA (D. melanogaster) and AgaCA (A. gambiae) for the CO₂ hydration reaction, at 20 °C¹⁹.

	KI [mM]^e
Inhibitor	hCA I^a	hCA II^a	DmBCA^b	AgaCA^c
F^−	>300	>300	0.80	9.42
Cl^−	6	200	0.97	8.74
Br^−	4	63	1.04	>200
I^−	0.3	26	1.18	>200
CNO^−	0.0007	0.03	0.73	9.46
SCN^−	0.2	1.6	1.28	6.41
CN^−	0.0005	0.02	0.67	8.34
N3^−	0.0012	1.5	1.12	12.40
HCO3^−	12	85	26.90	4.34
CO3^2−	15	73	0.86	9.25
NO3^−	7	35	43.74	6.50
NO2^−	8.4	63	28.60	4.55
HS^−	0.0006	0.04	1.01	25.10
HSO3^−	18	89	1.29	>200
SO4^2−	63	>200	1.36	9.03
ClO4^−	>200	>200	>200	>200
SnO3^2−	0.57	0.83	nt	1.80
SeO4^2−	118	112	nt	9.41
TeO4^2−	0.66	0.92	nt	4.96
P2O7^4−	25.8	48.5	nt	8.52
V2O7^4−	0.54	0.57	nt	7.98
B4O7^2−	0.64	0.95	nt	7.95
ReO^4−	0.11	0.75	nt	>200
RuO^4−	0.10	0.69	nt	>200
S2O8^2−	0.11	0.084	nt	>200
SeCN^−	0.0085	0.086	nt	8.68
CS3^2−	0.0087	0.0088	nt	8.19
Et2NCS2^−	0.79	3.1	nt	0.65
H2NSO2NH2	0.31	1.13	0.15	0.054
H2NSO3H^d	0.021	0.39	2.45	0.021
Ph-B(OH)2	58.6	23.1	22.39	0.047
Ph-AsO3H2^d	31.7	49.2	32.60	0.084

^a From ref.^20a.

^b From ref.⁹.

^c This work.

^d As sodium salt; nt: not tested.

^e Errors in the range of 5–10% of the shown data, from three different assays, by a CO₂ hydration stopped-flow assay¹⁹.

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