Differential Inhibition of Human Serum Cholinesterase with Fluoride: Recognition of Two New Phenotypes

Abstract

IT has been shown that individuals excessively sensitive to the drug suxamethonium have a reduced level of serum cholinesterase activity, and that this peculiarity is genetically determined¹. It has also been found that the cholinesterase present in the serum of such suxamethonium-sensitive individuals is qualitatively different from that occurring in most normal people². This difference can be most simply demonstrated by determining the degree of inhibition produced by certain anticholinesterase substances. For example, using 5 × 10⁻⁵ M benzoylcholine as substrate and 10⁻⁵ M dibucaine as inhibitor under standard conditions, the enzyme in most normal sera shows about 80 per cent inhibition, while that in sera from suxamethonium-sensitive individuals shows only about 20 per cent inhibition. The percentage inhibition obtained under these conditions has been called the dibucaine number (D.N.) and this appears to be a constant characteristic for any one individual³.