Sakata_1994_Pestic.Biochem.Physiol_50_247

Several forms of carboxylesterase were observed in a malathion-resistant small brown planthopper, Laodelphax striatellus Fallen, by isoelectrofocusing. To study the mechanisms of increased esterase activity, esterases were purified and their biochemical characteristics were investigated in five active esterase isozymes of two resistant strains. These esterases have polymorphic characteristics and their molecular weights ranged from 66 to 70 kDa, due to variations in glycosylation. The pI values of these esterases ranged from 5.3 to 4.7. These esterases were immunologically related and NH2-terminal amino acids were identical in all isozymes regardless of pI or molecular weight. No differences have been found in kinetic parameters (Km and Vmax) to alpha-naphthylacetate and specific activity toward alpha-naphthylacetate and malathion as a substrate in all isozymes. Resistant individuals showed high ali- and malathion carboxylesterase activities and these enhancements were caused by quantitative differences of carboxylesterases with several different pI.