Biology – Mode of action of enzymes | e-Consult

A colorimeter is an instrument used to measure the absorbance of light by a solution. In the context of enzyme-catalysed reactions involving colour changes, the principle relies on the fact that the product of the reaction absorbs light at a specific wavelength. As the enzyme catalyzes the reaction, the concentration of this coloured product increases. This increase in product concentration leads to a corresponding increase in the absorbance of the solution at the characteristic wavelength.

The relationship between absorbance and enzyme concentration is directly proportional, following Beer-Lambert's Law: A = εbc, where:

• A is the absorbance.
• ε is the molar absorptivity (a constant specific to the substance at a given wavelength).
• b is the path length of the light beam through the solution.
• c is the concentration of the absorbing species (in this case, the coloured product).

Therefore, by measuring the absorbance of the solution over time, we can indirectly monitor the rate of the enzyme-catalysed reaction. A higher absorbance indicates a higher concentration of the coloured product, signifying a faster reaction rate. The colorimeter measures the light transmitted through the sample, and the instrument calculates the absorbance based on the light absorbed.