title: Methodological principles in the enzymatic determination of substrates illustrated by the measurement of uric acid.
abstract: The enzymatic method of Haeckel for the determination of uric acid in serum has been used to compare three different kinetic approaches with the corresponding equilibrium (end-point) procedure. The kinetic methods were: measurement of the difference in absorbance between two pre-selected fixed instants during the course of the reaction under first-order conditions; measurement of the initial rate of reaction at substrate concentrations sufficiently low for first-order kinetics to apply, and determination of initial rate with substrate concentrations approximating to, or greater than, the Michaelis constant (pseudo-zero order kinetics). In the third method results were obtained by solving the Michaelis-Menten equation. The results emphasise the superiority of the two-point kinetic approach, which is apparent even when the timed absorbance values are obtained from an analogue signal displayed on a recorder chart. Conditions are described for the determination or uric acid in serum according to this principle.
mesh_terms: D004796:Clinical Enzyme Tests / Q000379:methods*; D006801:Humans; D007700:Kinetics; D013379:Substrate Specificity; D014503:Urate Oxidase / Q000378:metabolism; D014527:Uric Acid / Q000097:blood*
chemical_list: D014527:Uric Acid; D014503:Urate Oxidase