Comparative study of acetylcholinesterase and butyrylcholinesterase in brain and serum of several freshwater fish: specific activities and in vitro inhibition by DDVP, an organophosphorus pesticide

Abstract

A comparative study of specific activities and in vitro inhibition of brain and serum acetylcholinesterase (AChE; EC 3.1.1.7) and serum butyrylcholinesterase (BChE; EC 3.1.1.8) by DDVP, an organophosphorus pesticide, was conducted in 11 freshwater teleost species belonging to four families (Cyprinidae: common carp Cyprinus carpio, bream Abramis brama, blue bream A. ballerus, white bream Blicca bjoerkna, roach Rutilus rutilus, bleak Alburnus alburnus, ide Leuciscus idus; Percidae: perch Perca fluviatilis, pikeperch Stizostedion lucioperca; Esocidae: pike Esox lucius and Coregonidae: whitefish Coregonus albula). Specific AChE and BChE activities in brain and serum of fish were determined. Brain AChE activity varied among fish species ≈10-fold, ranging from 192.6 to 1353.2 μmol g⁻¹ h⁻¹, respectively in perch and whitefish. All cyprinids had higher brain AChE activity than those of other fish families. Serum AChE activity was 100-fold lower than in brain. Serum BChE activity was found only in cyprinids with the exception of the common carp. It varied from 163.8 to 970.3 μmol g⁻¹ h⁻¹, respectively in roach and bleak. The bimolecular enzyme inhibition rate constants (k_IIs) and pI₅₀ values for DDVP were calculated. Sensitivity of fish AChEs both in brain and serum is similar to those of typical AChEs in mammals. The range of k_IIs was 3.4–51.7×10³ mol⁻¹ l min⁻¹ (pI₅₀s were 5.3–6.5), respectively in white bream and ide. In contrast, fish serum BChE was more sensitive to inhibition than typical BChE and AChE in mammals. Values of k_II for BChE were 1.0–2.5×10⁷ mol⁻¹ l min⁻¹ (pI₅₀ was 8.8–9.2), respectively in ide and bleak.