A Proposed Principle of Kinetic-Thermodynamic Coupling in the Glycolytic Pathway and Its Application to the Regulation of Glycolysis by PKM2

Metabolic regulation is governed by two fundamental principles: enzyme kinetics and chemical thermodynamics. These principles play distinct yet complementary roles—thermodynamics determines the energetic favorability of reactions, while kinetics governs the rates at which those reactions proceed. Glycolysis has long served as a classical model for studying these mechanisms; however, the interaction between kinetics and thermodynamics, specifically how the pathway maintains stable flux and metabolite levels under perturbation, remains underexplored. Here, I propose a principle of kinetic-thermodynamic coupling in the glycolytic pathway. This principle explains how reaction rates, intermediate concentrations, and Gibbs free energy (ΔG) are coordinated such that equal flux is sustained through each enzymatic step. Using PKM2 as an illustrative example, the framework reveals how PKM2 activity, intermediate concentrations, Gibbs free energy values, and glycolytic rate are intricately coordinated, allowing the pathway to maintain flux continuity during transitions between steady states. Mathematical expressions are derived that link PKM2 activity to the thermodynamic structure of glycolysis, quantify its flux and concentration control coefficients, and define the mass transfer, duration, and average rate associated with the transient interstate phase. This coupling enables glycolysis to transition rapidly—within a fraction of a millisecond—between distinct steady states with minimal disruption. Together, the principle presented here unveils that glycolysis is not only responsive but intrinsically self-stabilizing, capable of maintaining homeostasis despite variations in enzyme activity, and it offers a novel biochemical perspective that fills a critical gap in our understanding of glycolytic regulation.