Muscle esterases of the mosquitofish, Gambusia affinis

1. Muscle esterases of Gambusia affinis were separable into 14 electrophoretic bands that formed five groups according to differential physical and chemical properties. 2. Nine phenotypic patterns were observed among the populations sampled, based on variation within the EST-3 group of carboxylesterases. 3. A model for the molecular and genetic bases of the EST-3 polymorphism was proposed on the basis of phenotypic patterns and physicochemical characterization. 4. The isozymes of EST-3 are inferred to be dimeric molecules on the basis of electrophoretic patterns observed following incubation of the EST-3 enzymes with neuraminidase. 5. The binding of sialic acid is believed to be an epigenetic mechanism which operates to maintain the structural integrity of these enzymes.