Calculate reaction velocity based on concentration changes over time
Seconds
Minutes
Absorbance Units (OD)
Millimolar (mM)
Micromolar (µM)
mg/dL
Moles
Please enter valid numerical values. Time cannot be zero.
Total Change ($\Delta y$): 0
Reaction Rate: 0
Note: The rate represents the slope of the reaction curve ($m = \Delta y / \Delta x$).
function calculateEnzymeRate() {
var initialVal = document.getElementById('initialValue').value;
var finalVal = document.getElementById('finalValue').value;
var timeVal = document.getElementById('timeElapsed').value;
var timeUnit = document.getElementById('timeUnit').value;
var measureUnit = document.getElementById('measureUnit').value;
var resultBox = document.getElementById('resultDisplay');
var errorBox = document.getElementById('errorDisplay');
// Reset displays
resultBox.style.display = 'none';
errorBox.style.display = 'none';
// Validation
if (initialVal === "" || finalVal === "" || timeVal === "") {
errorBox.innerHTML = "Please fill in all required fields.";
errorBox.style.display = 'block';
return;
}
var y1 = parseFloat(initialVal);
var y2 = parseFloat(finalVal);
var t = parseFloat(timeVal);
if (isNaN(y1) || isNaN(y2) || isNaN(t)) {
errorBox.innerHTML = "Inputs must be valid numbers.";
errorBox.style.display = 'block';
return;
}
if (t <= 0) {
errorBox.innerHTML = "Time elapsed must be greater than zero.";
errorBox.style.display = 'block';
return;
}
// Calculation Logic
// Calculate the absolute change in value (Product produced or Substrate consumed)
// Usually rate is reported as a positive value regardless of whether substrate decreases or product increases
var delta = Math.abs(y2 – y1);
// Calculate Rate
var rate = delta / t;
// Formatting Results
var deltaFormatted = delta.toFixed(4);
var rateFormatted = rate.toFixed(5);
// Determine unit string
var rateUnitString = measureUnit + "/" + timeUnit;
// Update DOM
document.getElementById('deltaValue').innerHTML = deltaFormatted + " " + measureUnit;
document.getElementById('rateValue').innerHTML = rateFormatted + " " + rateUnitString;
resultBox.style.display = 'block';
}
How to Calculate Rate of Enzyme Activity
Calculating the rate of enzyme activity is a fundamental task in biochemistry and molecular biology. The rate of reaction, often referred to as the reaction velocity ($v$), measures how fast an enzyme converts a substrate into a product. This metric is crucial for understanding enzyme kinetics, inhibition, and metabolic control.
The Formula for Reaction Rate
In its simplest form, the rate of an enzymatic reaction is defined as the change in the amount of reactant or product per unit of time. It mathematically represents the slope of the linear portion of the reaction progress curve.
Rate = | Final Concentration – Initial Concentration | / Time Elapsed
Where:
Concentration ($y$): This is the measured variable, often Absorbance (Optical Density) from a spectrophotometer, or molar concentration (mM, µM).
Time ($t$): The duration over which the change in concentration was observed.
Step-by-Step Calculation Guide
Obtain Initial Reading: Measure the concentration of product or absorbance at the start of the linear phase ($t_0$).
Obtain Final Reading: Measure the concentration or absorbance after a specific time interval ($t_{final}$).
Calculate Delta ($\Delta$): Subtract the initial value from the final value. Use the absolute value to ensure a positive rate.
Divide by Time: Divide the change in value by the total time elapsed.
Example Calculation
Imagine you are running an assay to test the activity of Alkaline Phosphatase. You measure the production of p-Nitrophenol by monitoring absorbance at 405nm.
Initial Absorbance ($A_1$): 0.105 OD
Final Absorbance ($A_2$): 0.655 OD
Time Elapsed: 2 minutes
Step 1: Calculate Change in Absorbance ($\Delta A$) = $|0.655 – 0.105| = 0.550$ OD
When calculating rates, it is vital to keep environmental conditions constant, as they significantly impact the velocity:
Temperature: Reaction rate generally increases with temperature until the enzyme denatures.
pH: Every enzyme has an optimum pH range; deviating from this reduces activity.
Substrate Concentration: The rate increases with substrate concentration until the enzyme becomes saturated ($V_{max}$).
Converting Absorbance to Concentration
While the calculator above provides the rate in terms of your input units (e.g., Absorbance/min), scientists often need the rate in Molar units (e.g., $\mu mol/min$). To do this, you utilize the Beer-Lambert Law:
$A = \epsilon \cdot l \cdot c$
Where $\epsilon$ is the molar extinction coefficient and $l$ is the path length (usually 1 cm). By dividing your calculated Absorbance Rate by the extinction coefficient, you can convert the rate into concentration units ($M/min$).