Manual Colorimetric Methods for Pseudocholinesterase and Red Cell (True) Cholinesterase

Abstract

Abstract This report describes both an improved version of Garry and Routh’s colorimetric assay for serum pseudocholinesterase [Clin. Chem. 11, 91 (1965)] and a variation of this method for use in measuring cholinesterase in red cells. These procedures require either 0.1 ml of serum (diluted 10-fold) cr 0.1 ml of packed, heparinized erythrocytes (diluted 100-fold). The reaction involves the hydrolysis of acetylthiocholine to acetic acid and thiocholine, and the quantitation of the thiocholine with 5,5'-dithiobis-2-nitrobenzoic acid. In the procedure, the sample of diluted serum or cells is added to the combined buffer—color-substrate reagent at 37°C. After incubation for 10 min, quinidine sulfate is added to retard the reaction and the color is read at 450 nm. Blanks are required with each red cell sample, but not for sera. The results correlate well with those obtained by Michel’s standard ΔpH assay, Kalow’s benzoylcholine uv-rate reaction, Caraway’s colorimetric procedure, and Ellman’s colorimetric rate reaction. A method for determination of dibucaine-inhibited serum pseudocholinesterase is also described.