Improved method for the identification of the fluoride-resistant plasmacholinesterase genotypes

This investigation was prompted by the findings that (1) dibucaine-resistant homozygotes and heterozygotes for plasmacholinesterase also exhibit resistance to fluoride inhibition, (2) the differentiation of dibucaine-resistant from the fluoride-resistant genotypes is ambiguous with the method of Harris and Whittaker, (3) the plasmacholinesterase inhibition by Na fluoride (FN) is markedly influenced by the temperature. Therefore, we modified their method by increasing (1) the temperature of the reaction from 25C to 37C and (2) the concentration of Na fluoride from 5.0 x 10(-5) M to 2.5 x 10(-4) M. With this method, gentically normal individuals have a mean FN + or - SD equals 43.0 + or - 10.0 and atypical dibucaine-resistant heterozygotes 67.0 + or - 5.37. Since a linear correlation was observed between DN and FN by our new method, a fluoride number 2 SD lower than the predicted FN from the DN can distinctly identify the fluoride-resistant plasmacholinesterase genotype Ef.