The reactions of serum cholinesterase with organic cations,
such as decamethonium and atropine, as well as with inorganic
cations, such as Sc3+, Eu3+, and Yb3+, have been studied. Graphical
analysis of the inhibition of serum cholinesterase by decamethonium
and lanthanide ions revealed a linear mixed inhibition. Atropine
inhibited competitively serum cholinesterase with butyrylcholine or
acetylcholine as a substrate, whereas with benzoylcholine as ·a
substrate atropine increased the enzyme activity. The acceleration
of benzoylcholine hydrolysis by the simultaneous action of atropine
and EuCla was more pronounced than with atropine alone. The
concentrati0tn of EuCI3 which practically did not affect the
enzyme activity, decreased the inhibition of serum cholinesterase
by o-tubocurarine. It was suggested that the mixed type of
inhibition of serum cholinesterase by decamethonium and the
lanthanide ions, as well as the effect of the combined action of
organic cations and lanthanides on the enzyme activity, might
reflect the allosteric properties of serum cholinesterase
