SENSITIVITY OF ACETYLCHOLINESTERASE MOLECULAR-FORMS TO INHIBITION BY HIGH MGCL2 CONCENTRATION

Previous studies have shown that the asymmetric (A(12)) and the dimeri c (G(2)), but not the tetrameric (G(4)), acetylcholinesterase (AChE) f orms are inactivated by high MgCl2 concentration (Perelman and Inestro sa (1989) Anal. Biochem. 180, 227-230). Here we show that the effect o f MgCl2 on AChE activity corresponds to an irreversible inhibition and is not due to environmental effects related to the different extracti on media. The anchor domain in each AChE form was not involved in the differential MgCl2 sensitivity. Monomers derived from the various AChE forms behave in a way similar to that of the original assembled forms . Purified AChE molecular forms showed the same sensitivity to MgCl2, than the same enzyme forms studied in tissue extracts. Neither the aff inity for the substrate nor the inhibition by excess substrate of the residual AChE activity were affected by high MgCl2 concentration. Resu lts indicate that the differences between the tetrameric enzyme and th e other two AChE molecular forms occur at the level of the catalytic s ubunit, probably due to differential post-translational processing.