Allosteric Regulation Keeps Glycolysis Running Steady, Model Reveals

Every time a cell burns glucose for energy, it runs through one of the most ancient chemical sequences in biology - a ten-step cascade called glycolysis that predates the appearance of oxygen in Earth's atmosphere by more than a billion years. Yet despite glycolysis being studied intensively for over a century, scientists lacked a detailed, biophysically rigorous model of how the pathway actually regulates itself. That gap has now been filled.

Denis V. Titov and colleagues at the University of California, Berkeley have constructed the first comprehensive biophysical model of glycolysis, built from the ground up using decades of laboratory measurements. The work earned Titov the 2025 Biophysical Journal Paper of the Year Award for Early Career Investigators, presented at the 70th Annual Meeting of the Biophysical Society in San Francisco in February 2026.

Why Glycolysis Resists Easy Modeling

Glycolysis converts one molecule of glucose into two molecules of pyruvate, yielding a net gain of two ATP molecules in the process. The pathway must keep working across an enormous range of conditions - a sprinting muscle cell demands ATP at roughly 100 times the rate of a cell sitting idle - while also supplying precursor molecules for lipid synthesis, amino acid production, and dozens of other biosynthetic routes. That dual role creates a fundamental tension: the pathway must run fast when needed but must also resist spiraling into an uncontrolled cascade that chokes cells with intermediate molecules.

Mathematical models of glycolysis have existed since the 1960s, but they tended to be simplified, relying on sweeping assumptions and a handful of adjustable parameters. Due to the complexity of glycolysis and experimental challenges, much of our understanding of glycolytic regulation has come from mathematical models - but those models were scarce and simplified.

172 Parameters, Dozens of Datasets

Titov's team took a different approach. Rather than simplifying, they assembled a system of differential equations capturing the kinetics of each glycolytic enzyme in quantitative detail. The central challenge was parameter estimation: the model required fitting 172 parameters simultaneously to data drawn from dozens of published in vitro experiments.

That is a notoriously difficult computational problem. Parameter spaces of this size are riddled with local minima, and small errors in one parameter can cascade into large errors elsewhere. The team developed methods to navigate this space and arrive at a parameter set consistent with the breadth of available experimental data.

Two results stood out. First, the model showed that basic mass action kinetics - the straightforward relationship between reactant concentrations and reaction rates - are sufficient on their own to maintain the high and stable free energy of ATP hydrolysis that cells depend on. The ATP system does not require any exotic regulatory architecture just to hold its energy charge steady.

Second, and perhaps more importantly, the model revealed that allosteric regulation is not optional. Allosteric regulation refers to the process by which a molecule binds to a site on an enzyme distant from its active site and changes the enzyme's behavior. In glycolysis, several enzymes are known to be allosterically regulated by ATP, ADP, and inorganic phosphate - the very molecules whose concentrations signal the cell's energy state. Remove that regulation from the model, and glycolytic intermediates begin accumulating without bound.

A Built-in Overflow Valve

The finding clarifies why evolution preserved allosteric regulation in glycolytic enzymes across all domains of life, from bacteria to human cells. It functions as an overflow valve. When ATP is plentiful and the cell doesn't need more energy immediately, rising ATP concentrations directly inhibit phosphofructokinase - one of glycolysis's key control points - slowing the entire pathway before intermediates pile up. When ATP drops, that inhibition lifts and the pathway accelerates. The model captures these dynamics quantitatively for the first time at the whole-pathway level.

Vasanthi Jayaraman, Editor-in-Chief of Biophysical Journal, called the work "a detailed and experimentally grounded model of glycolysis" that "sets an important benchmark for the field and will shape how we think about cellular energy metabolism going forward."

A Platform for Future Metabolic Research

The model was published in Volume 124, Issue 10 of Biophysical Journal. As a validated quantitative framework, it gives researchers a testable platform for exploring how glycolysis responds to genetic mutations associated with cancer and metabolic diseases, how it is perturbed by drugs, and how it contributes to the altered energy metabolism characteristic of tumor cells.

Some caveats apply. The model is built from in vitro kinetic measurements - experiments conducted on purified enzymes in controlled buffer conditions that may not fully capture the complex, crowded environment of a living cell, where enzymes may interact with scaffolding proteins and operate under different pH and ion concentrations. Whether the parameter values hold precisely inside cells remains to be validated through follow-up experiments in intact biological systems.

Still, the model represents a meaningful advance. By demonstrating that allosteric regulation is mechanistically necessary - not merely redundant - to prevent intermediate accumulation, it places a long-standing piece of cell biology on a firm quantitative footing. For a pathway that underpins energy production in virtually every living organism on Earth, that is a significant step toward understanding how life manages its most fundamental chemistry.