Involvement of sulfhydryl groups in time-dependent changes of diaphragm acetylcholinesterase activity by monovalent (Na+, Li+) cations.

Acetylcholinesterase (AChE) activity, as a function of time, showed a concentration dependent increase induced by NaCl, followed by a plateau. In the presence of LiCl, the enzyme activity, before its stabilization, presented an increase, followed by a decrease to a minimum value. Sucrose increased the initial rise and the final value of AChE activity and caused no changes, as a function of time, in the absence of cations. Moreover sucrose eliminated AChE activity decrease caused by LiCl. 2-mercaptoethanol induced considerable and steady increase of AChE activity, in the presence or absence of cations or sucrose and no changes, as a function of time. These results show an activating and protecting effect of sucrose on AChE and the possible involvement of sulfhydryl (SH) groups in the time-dependent changes of the enzyme activity induced by Na+ or Li+.