A source of error in the determination of inhibitor constants of serum cholinesterase.

The effect of temperature on the inhibition of serum cholinesterase by dibucaine, fluoride and chloride has been studied. It is found that the dibucaine and chloride numbers together are capable of differentiating the inherited enzyme variants at 30° and 37°C. Fluoride numbers contribute little information at these temperatures; indeed fluoride inhibition is so sensitive to temperature change that unless rigid temperature control is maintained in current techniques, erroneous conclusions may be drawn. A family with unusual chloride numbers is revealed.