Identification of Serum Cholinesterase Fluoride Variants by Differential Inhibition in Tris and Phosphate Buffers

Abstract

We describe a useful technique to identify "fluoride-resistant" serum cholinesterase variants (E₁^uE₁^f and E₁^fE₁^f) by using the method of Garry to detect "atypical" variants and to measure serum cholinesterase activity [Clin. Chem. 17, 192 (1971)]. With butyrylthiocholine as substrate, sodium fluoride is used as a differential inhibitor in both Tris and phosphate buffer systems (50 mmol/liter, pH 7.4, 25°C). Fluoride inhibition values are plotted on two-dimensional graph paper, Tris plus sodium fluoride vs. phosphate plus sodium fluoride. Inhibition values for the "fluoride-resistant" and "atypical" variants are located in specific quadrants, which permits unequivocal identification of each variant. Examination of 836 Caucasian preschool children revealed a gene frequency of 0.0066 for the "fluoride" variant. No "fluoride-resistant" variants were found in 168 Negro preschool children examined.