CHANGES CAUSED BY METHIDATHION IN ACTIVITY AND DISTRIBUTION OF MOLECULAR-FORMS OF CARP (CYPRINUS-CARPIO L) ACHE

The activity and molecular forms of acetylcholinesterase (AChE, EC 3.1 .1.7) were characterized in the heart and skeletal muscle of carp (Cyp rinus carpio L.) exposed to 2 mg/liter of the insecticide methidathion (MD; xy-2-oxo-1,3,4-thiodiazol-3-yl-methyl-O,O-dimethyl phosphodithio ate) for 5 days at a water temperature of 12 +/- 1 degrees C. The spec ific activity of the heart AChE (4.78 +/- 2.14 x 10(-2) U/mg protein) was higher than that of the muscle AChE (2.53 +/- 0.75 x 10(-2) U/mg p rotein) in control carp. The solubility properties and molecular forms of the AChE in the two tissues were studied by extraction in high-sal t medium (1 and 0.4 M NaCl) with and without Triton X-100. The ratio o f membrane-bound to salt-soluble forms of AChE was higher in the muscl e than in the heart. Velocity sedimentation centrifugation revealed th at the skeletal muscle and the heart contained three molecular forms: G(4), A(4), and A(12). After the in vivo exposure of fish to MD, the A ChE activity decreased significantly (77-99%) in the tissues investiga ted. Furthermore, the relative distribution of the AChE molecular form s differed somewhat from that in the control fish. Form G(l) became de tectable after the treatment, but could not be measured in the control tissues. The proportions of the other forms decreased by a few percen tages. The accumulation of MD was studied in seven organs: the brain, heart, intestine, kidney, liver, muscle, and roe. The liver and roe ha d the highest MD contents, and the heart and muscle had the lowest. Th is study shows the MD not only blocks the activity of AChE, but also m odifies the distribution of its molecular forms. (C) 1995 Academic Pre ss, Inc.