An investigation of the carbonic anhydrase inhibitor in eel plasma.

1. Carbonic anhydrase activity in blood and gill from freshwater and seawater acclimated European eels, Anguilla anguilla has been determined. 2. Plasma from freshwater and seawater eels possess a potent inhibitor of erythrocytic carbonic anhydrase, in agreement with previous investigations on freshwater fish. 3. The plasma inhibitor is equally effective against gill and gut carbonic anhydrase from the eel. Although not as potent, the eel inhibitor is also effective against CA from rainbow trout. The inhibitor was without effect on bovine-CA. 4. The inhibitor is heat-PCA- and trypsin-labile. It is also non-dialyzable and insensitive to concanavalin A. Using gel filtration, the inhibitor appears to be a fairly small molecular weight protein approximately 10,000-30,000.