Evaluation of the Hill Coefficient for Yeast Aspartate Transcarbamylase by Nonlinear Regression Analysis

Primary data for yeast aspartate transcarbamylase reported by Kaplan et al. ((1967) Arch. Biochem. Biophys. 119, 541–551) have been evaluated for the degree of fit to hyperbolic and sigmoidal functions. The restricted nature of their experimental design does not provide an adequate basis for discrimination between the types of mechanisms considered. Comparison of the parameter estimates obtained by the Hill plot and by nonlinear regression analysis demonstrated that the Hill plot may give rise to gross errors in the determination of the kinetic constants.