Table 1.

Higher vertebrate α-CA isozymes, their relative CO₂ hydrase activity, affinity for sulphonamide inhibitors and subcellular location

Isozyme	Catalytic activity (CO2 hydration)	Affinity for sulphonamides	Subcellular location
CA I	Low (10% of that of CA II)	Medium	Cytosol
CA II	High	Very high	Cytosol
CA III	Very low (1% of that of CA II)	Very low	Cytosol
CA IV	High	High	Membrane bound
CA V	Moderate-high	High	Mitochondria
CA VI	Moderate	Medium-low	Secreted into saliva
CA VII	High	Very high	Cytosol
CA VIII	Acatalytic	Not measured	Probably cytosolic
CA IX	High	Unknown	Membrane bound
CA X	Acatalytic	Not measured	Unknown
CA XI	Acatalytic	Not measured	Unknown
CA XII	Low	Unknown	Membrane bound
CA XIII	Probably high	Unknown	Unknown
CA IV	Low	Unknown	Membrane bound

Reproduced with permission from Supuran & Scozzafava (2000).