On the cholinesterase inhibiting properties of two pyrrolidine derivatives

The influence of cis-2-phenyl-1-pyrrolidino-cyclohexane (RX 67 668) and of cis-2-(3-hydroxyphenyl)-1-pyrrolidino-cyclohexane methobromide (RX 72 601) on acetylcholinesterase (AChE) and plasma cholinesterase (ChE) was investigated in vitro by means of a photometric assay technique with respect to their mechanism and constants of inhibition. The two compounds cause reversible inhibition of both AChE and ChE, the (I)50 and Ki for RX 67 668 being 2.5 x 10(-5) M and 4 x 10(-6) M (AChE), resp., and 2.0 x 10(-5) M and 8 x 10(-7) M (ChE), resp.; and for RX 72 601 7.9 x 10(-8) M and 3 x 10(-9) M (AChE), resp., and 3.2 x 10(-7) M and 1 x 10(-8) M (ChE), resp. The kinetic analysis of the inhibitory action disclosed a purely competitive mechanism. The inhibition of the two esterases is assumed to be induced by the formation of a readily dissociable enzyme-inhibitor complex due to the binding of the positively charged pyrrolidine moiety of the two substances to the anionic subsite of the active center, thus impairing the formation of an enzyme-substrate complex.