Influence of ketamine on human plasma cholinesterase.

The influence of ketamine upon human plasma cholinesterase (E.C. 3.1.1.8) was determined by means of a colorimetric assay technique at 25 degrees C, pH 7.7 with butyrylthiocholine as substrate. Ketamine caused a reversible inhibition of cholinesterase (pI50= 2.75; apparent Ki=4.94X10(-4) M). The kinetic analysis of the inhibitory action revealed a mixed competitive/non-competitive type of mechanism with a prevalence of the non-competitive component (alpha-value = 4.9). A decrease in cholinesterase activity is thought to be a result of conformational change of the enzyme protein which is induced by a reversible binding of ketamine to anionic side receptors in the vicinity of the active centre.