Studies on cholinesterase. 7. Determination of the molar concentration of pseudo-cholinesterase in serum

Abstract

Exptl. results showed that Nu683 (dimethyl-carbamate of [2-hydroxy-5-phenylbenzyl] -trimethyl-ammonium bromide) acted as a reversible competitive inhibitor of pseudo-cholinesterase and combined specifically with the pseudo-cholinesterase active center on an equimolar basis. The ratio of E/K1 was found to have a value appreciably greater than 0.1; this made it possible to determine pseudo-cholinesterase concn. in serum accurately by a method which appeared to be completely justified theoretically. The advantages of this method over those used previously were discussed. The exptl. results obtained with this inhibitor showed sufficiently good agreement with the theoretical predictions of Straus and Goldstein (1943) and Goldstein (1944) to provide exptl. confirmation of the concept of 3 zones of inhibitor action. The pseudo-cholinesterase concns. were expressed on the basis of enzyme activity under standard conditions. The concn. of pseudocholinesterase in the particular samples of full serum used were as follows: horse serum 8.8 x 10-8 [image]; human serum, 7.9 x 10-8 [image]; female mouse serum, 5.8 x 10-8 [image]; dog serum, 4.6 x 10-8 [image]; female rat serum, 1.7 x 10-8 [image]. The pseudo-cholinesterases from mouse, rat, horse, human and dog serum formed a series in which the ratio of pseudo-cholinesterases activity towards 0.06 [image] acetylcholine over that towards 0.006 [image] benzoylcholine diminished progressively from 8.2 to 1.6. In this same series, the absolute activity of the pseudo-cholinesterases towards acetylcholine became progressively smaller. Other characteristics of the pseudo-cholinesterases also varied considerably from one type of pseudo-cholinesterase to another, but did not show any correlation to the above series. The significance of these results was discussed with respect to the concept of the pseudo-cholinesterases as a special group of closely related enzymes.