THE CARBONIC-ANHYDRASE INHIBITOR IN TROUT PLASMA - PURIFICATION AND ITS EFFECT ON CARBONIC-ANHYDRASE ACTIVITY AND THE ROOT EFFECT

The plasma inhibitor of carbonic anhydrase (CA) from rainbow trout was purified using ion exchange chromatography. The inhibitor has a high isoelectric point value (pI > 10). SDS-PAGE electrophoresis and gel filtration demonstrated that the inhibitor is a low molecular weight compound of about 6,000 daltons. The plasma inhibitor was more effective against gill CA than against blood CA in vitro, probably reflecting the presence of various CA-isoenzymes in red blood cells and gill tissue. The apparent Root effect, i.e., the impairment of the oxygen binding capacity of hemoglobin in red blood associated with increased blood P was counteracted by the plasma inhibitor, probably by acting on membrane-bound and/or cytosolic blood CA. This interaction may be of importance in adaptive mechanisms, e.g., during the acidemic phase, when the fish is being acclimated to hypercapnic conditions.