ACTIVITY OF ESTERASES FROM DIFFERENT TISSUES OF FRESH-WATER FISH AND RESPONSES OF THEIR ISOENZYMES TO INHIBITORS

Activity of nonspecific esterase from different tissues (i.e., liver, gallbladder, heart, intestine, and muscle) of five species of freshwat er fish, namely, topmouth gudgeon (Pseudorasbora parva), goldfish (Car assius auratus), nile tilapia (Tilapia nilotica), mosquitofish (Gambus ia affinis), and rainbow trout (Salmo gairdneri) was tested using alph a-naphthyl acetate as substrate. The results indicated that activity o f the enzyme was mainly concentrated in the digestive system (i.e., in testine, liver, bile). The overall activity was highest in nile tilapi a, followed by mosquitofish, topmouth gudgeon, goldfish, and lowest in rainbow trout. Electrophoresis and the following in vitro treatment o f the isoenzymes with triphenol phosphate (TPP, an inhibitor of carbox ylesterase) indicated the TPP-sensitive esterase was mainly distribute d in liver of the five species. The enzyme was not found in the other five tissues (including gill) except in gallbladder of topmouth gudgeo n and goldfish. The correlation was obviously improved between suscept ibility and detoxification capacity if activity of the TPP-sensitive e sterase was employed instead of that of the nonspecific esterase to ma ke the comparison. In vitro treatment of nonspecific esterase in liver with malaoxon proved that the active metabolite of malathion inhibite d a different isoenzyme from the TPP-sensitive one.