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- Title
Model Analysis of the Apparent Saturation Kinetics of Purine Nucleobase Uptake in Cells co-Expressing Transporter and Metabolic Enzyme.
- Authors
Suzuki, Satoru; Inoue, Katsuhisa; Tamai, Ikumi; Shirasaka, Yoshiyuki
- Abstract
Purpose: This study aims to understand the effect of salvage enzyme activity on the saturable kinetics of facilitated cellular uptake of purine nucleobase by developing a cellular kinetic model incorporating equilibrative nucleobase transporter 1 (ENBT1) and adenine phosphoribosyltransferase (APRT), with adenine as a model nucleobase. Methods: A cellular kinetic model incorporating the functions of ENBT1 and APRT was developed using Napp software and employed for model-based analysis of the cellular disposition of adenine. Results: Simulation analysis using the developed cellular kinetic model could account for the experimentally observed time-dependent changes in the Km(app) value of adenine for ENBT1-mediated uptake. At a long experimental time, the model shows that uptake of adenine is rate-limited by APRT, enabling determination of the Km value for APRT. At early time, the rate-limiting step for adenine uptake is ENBT1-mediated transport, enabling determination of the Km value for ENBT1. Further simulations showed that the effect of experimental time on the Km(app) value for ENBT1-mediated uptake is dependent on the APRT expression level. Conclusion: Our findings indicate that both enzyme expression levels and experimental time should be considered when using cellular uptake studies to determine the Km values of purine nucleobases for facilitated transporters.
- Subjects
ADENINE; CELL analysis; BASE pairs; ENZYMES
- Publication
Pharmaceutical Research, 2021, Vol 38, Issue 9, p1585
- ISSN
0724-8741
- Publication type
Article
- DOI
10.1007/s11095-021-03086-w