Human lens carbonic anhydrases. Purification and properties.

Abstract

To isolate and characterize carbonic anhydrase (CA) isozymes of human lenses. Affinity chromatography was used to separate CA isozymes, as monitored by an immunosorbent assay. Amino acid analysis was done on the antigenic CAII. CA catalytic activity and its sensitivity to inhibition was measured on soluble and membrane-bound CA isozymes. The lens contains 0.25, 9, and 2 microg/g wet weight of CAI, II, and III, respectively. Almost all of the CA catalytic activity originates from CAII. Plasma membranes had a CA activity that was inhibited like the membrane-bound isozyme CAIV CONCLUSIONS: CA activity in human lenses originates from CAI, II and III in the cytoplasm, and from CAIV at plasma membranes of lens epithelium and fibres. CA probably functions like CA in erythrocytes, by facilitating CO2 transport. CAII and CAIV are probably also involved in translenticular ion transport. Chronic intake of CA inhibitors does not seem to induce cataract formation.