[A kinetic study of the blood serum cholinesterase activity in the freshwater fish Abramis ballerus].

In reaction of hydrolysis of choline and thiocholine esters of carbonic acids at 25 degrees C, cholinesterase activity of the blood serum from the fish A. ballerus has been studied by modified Ellman's method and potentiometric titration method. The activity is maximal in pH region 7.5-9.0 and is not inhibited by high concentration of substrates. Michaelis constants and maximal rates for the enzyme reactions were determined. Butyrylcholine and butyrylthiocholine were hydrolyzed with the highest rates by the serum. Some of the organophosphorus inhibitors (diisopropylfluorphosphate and DDVF) inhibit cholinesterase activity of the blood serum significantly faster, whereas some of the carbamates (aminostygmin, eserine, etc.) inhibit it significantly slower than typical butyrylcholinesterase from horse blood serum and typical acetylcholinesterase of human erythrocytes. Besides, with respect to the sensitivity to inhibitors and some other properties, fish blood serum cholinesterase differs from other known cholinesterases.