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Metabolism and Enzymology

Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus^1,2

Department of Biology and Atlantic Institute of Biotechnology, Life Sciences Center, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1, Atlantic Institute of Biotechnology, 6093 South Street, Halifax, Nova Scotia, Canada B3H 1T2

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO₂ 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 CO₂ concentrations, and decreased at CO₂ saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO₃^– for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.

² AIB Publication No. 005.