Related Experiment Video
Updated: Jul 6, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
Published on: January 16, 2016
Allosteric kinetics of human carboxylesterase 1: species differences and interindividual variability
Shiori Takahashi1, Miki Katoh, Takashi Saitoh
1Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-1192, Japan.
Abstract:
Esterified drugs such as imidapril, derapril, and oxybutynin hydrolyzed by carboxylesterase 1 (CES1) are extensively used in clinical practice. The kinetics using the CES1 substrates have not fully clarified, especially concerning species and tissue differences. In the present study, we performed the kinetic analyses in humans and rats in order to clarify these differences. The imidaprilat formation from imidapril exhibited sigmoidal kinetics in human liver microsomes (HLM) and cytosol (HLC) but Michaelis-Menten kinetics in rat liver microsomes and cytosol. The 2-cyclohexyl-2-phenylglycolic acid (CPGA) formation from oxybutynin were not detected in enzyme sources from rats, although HLM showed high activity. The kinetics were clarified to be different among species, tissues, and preparations. In individual HLM and HLC, there was large interindividual variability in imidaprilat (31- and 24-fold) and CPGA formations (15- and 9-fold). Imidaprilat formations exhibited Michaelis-Menten kinetics in HLM and HLC with high activity but sigmoidal kinetics in those with low activity. CPGA formations showed sigmoidal kinetics in high activity HLM but Michaelis-Menten kinetics in HLM with low activity. We revealed that the kinetics were different between individuals. These results could be useful for understanding interindividual variability and for the development of oral prodrugs.
Related Concept Videos
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Introduction to Enzyme Kinetics
The experimenter can then plot the initial reaction rate or velocity (Vo) of a given trial against the substrate concentration ([S]) to obtain a graph of the reaction properties. For many enzymatic reactions involving a...
Enzyme Kinetics
Scientists typically study enzyme kinetics with a fixed amount of enzyme in the controlled environment of a test tube. When more reactant, or substrate, is...
Allosteric Regulation
Allosteric Regulation
Pharmacogenetics of Phase I Enzymes: Cytochrome P450 Isozymes

