Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus.

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO(2) concentrations and pretreated with carbonic anhydrase (CA) inhibitors, was determined using an air-suspension, differential infra-red gas analyzer technique. It was found that the CA inhibitors, acetazolamide, dextran-bound acetazolamide (DBI, which does not permeate cell membranes), and subtilisin (a protease that attacks the cell surface) inhibit photosynthetic carbon uptake in C. crispus. Inhibition was greatest at low CO(2) concentrations, and decreased at CO(2) saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO(3) (-) for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.