NON-LINEAR CALIBRATION OF AN ENZYMATIC AS SAY BY THE GENERALIZED LEAST-SQUARES METHOD - APPLICATION TO HUMAN SERUM ESTERASES

A variant of the GLS (Generalized Least Squares) method has been appli ed to the nonlinear calibration of the assay of two esterases in human serum: arylesterase (EC 3.1.8.1) and cholinesterase (EC 3.1.1.8). The curves relating the variations of enzyme activity to substrate concen tration were described by the Michaelis equation. The analytical error was expressed as a function of the measured activity by means of a po wer function. Using the measurements carried out in a group of healthy subjects, the GLS method matched both the Michaelis equation and the analytical error model, and determined the substrate concentration req uired to keep the coefficient of variation of the assay below 5%, in s pite of the wide variations of enzyme activities between subjects.