Sensitivity of acetylcholinesterase molecular forms to inhibition by high MgCl2 concentration

Previous studies have shown that the asymmetric (A12) and the dimeric (G2), but not the tetrameric (G4), acetylcholinesterase (AChE) forms are inactivated by high MgCl2 concentration (Perelman and Inestrosa (1989) Anal. Biochem. 180, 227-230). Here we show that the effect of MgCl2 on AChE activity corresponds to an irreversible inhibition and is not due to environmental effects related to the different extraction 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 affinity for the substrate nor the inhibition by excess substrate of the residual AChE activity were affected by high MgCl2 concentration. Results indicate that the differences between the tetrameric enzyme and the other two AChE molecular forms occur at the level of the catalytic subunit, probably due to differential post-translational processing.