A manometric assay was used to determine the carbonic anhydrase dehydration activity in the intact erythrocytes of the toad Bufo marinus (L). It was found that unwashed toad whole blood lacks dehydration activity in contrast to human whole blood. With the removal of the plasma and replacement with MacKenzie Toad Saline a pronounced dehydration activity was observed. This increase in enzyme activity was inhibited when the original plasma was replaced. An inhibitor in the plasma is thought to limit in vivo dehydration activity. Hemolysed red cells were seen to exhibit an increase in enzyme activity, both when the original plasma was present and when the red cells were suspended in toad saline. The plasma inhibitor could therefore work by inhibiting membrane bound CA or by inhibiting the influx of HCO₃ thus preventing dehydration activity. The lack of red cell dehydration activity would presumably alter CO₂ excretion patterns in the toad and the possible implications are discussed.
Desmar Walkes (Mon,) studied this question.