Delta G From Enzyme Kinetics
Delta G can connect enzyme kinetics with thermodynamic style comparisons. This calculator treats kcat and Km as practical kinetic inputs. It does not prove full reaction equilibrium. Instead, it gives useful apparent free energy values. The main output uses catalytic efficiency, kcat divided by Km. That value shows how strongly turnover and substrate binding work together.
Why This Estimate Matters
Enzyme studies often compare mutants, buffers, pH levels, or temperatures. Raw kcat values can rise while Km also rises. That mixed change may hide the real performance shift. Catalytic efficiency gives one combined number. A relative delta G then converts that ratio into energy language. Negative values suggest improved apparent performance versus the chosen reference. Positive values suggest weaker apparent performance.
The tool also reports an Eyring activation estimate from kcat. This barrier uses temperature and assumes kcat behaves like a rate constant. It is best viewed as a model estimate. It helps compare runs under similar assumptions. It should not replace calorimetry or full equilibrium work.
Inputs You Can Control
Enter kcat in per second. Enter Km in micromolar, millimolar, or molar units. Add temperature because RT changes with heat. Choose a reference catalytic efficiency for comparison. A reference of one is simple. A mutant or wild type value is often better. Add substrate concentration to estimate saturation and observed first order turnover. Add enzyme concentration to estimate initial velocity.
Reading The Results
The efficiency result uses molar units. The relative delta G uses negative RT times the natural log of efficiency over reference efficiency. When the ratio equals one, the relative value is zero. The activation estimate uses RT times the natural log of kBT over h kcat. Lower activation values usually mean faster turnover.
Use results as screening values. Keep units consistent. Compare only experiments measured under similar conditions. Temperature, buffer, isotope effects, and assay design can change interpretation. Export the table when you need records. The CSV file supports spreadsheets. The PDF file supports simple reporting. Good documentation also matters. Store every assumption beside each result. Record units, reference values, and assay notes. Small reporting gaps can make later comparisons confusing, especially during kinetic model review, manuscript preparation, and scientific work.