THE ACTION OF NORMAL AND ATYPICAL CHOLINESTERASE OF HUMAN SERUM UPON A SERIES OF ESTERS OF CHOLINE

Abstract

The results of a comparison of the actions of individual human sera support evidence previously obtained for the existence of two different types of pseudocholinesterase in man. Maximum rates of hydrolysis of choline esters by human sera containing the normal type of cholinesterase were two to four times greater than the maximum rates obtained with sera containing atypical esterase. Human sera with the normal type of cholinesterase hydrolyzed butyrylcholine at a considerably faster rate than pentanoylcholine; atypical esterase hydrolyzed pentanoylcholine at approximately the same rate as butyrylcholine. All Michaelis constants for the normal enzyme were lower than those for the atypical enzyme by a factor which varied from 1.4 to 6.4. The data were compatible with the assumption of a linear relationship between the log of the Michaelis constants and the number of acyl carbons in the choline esters, but the slopes differed significantly for the two enzymes. For a homologous series of choline esters, there was no correlation between rates of hydrolysis and Michaelis constants.