What is the unit for measuring enzyme activity? What is turnover number
Enzyme activity = moles of substrate converted per unit time = rate × reaction volume. Enzyme activity is a measure of the quantity of active enzyme present and is thus dependent on conditions, which should be specified. The SI unit is the katal, 1 katal = 1 mol/second, but this is an excessively large unit.
In enzymology, turnover number (also termed kcat) is defined as the maximum number of chemical conversions of substrate molecules per second that a single catalytic site will execute for a given enzyme concentration [ E T ]
The unit for measuring enzyme activity is typically expressed in international units (IU), which represents the amount of enzyme that catalyzes a specific reaction under specific conditions. To determine the enzyme activity, you can perform an enzymatic assay where the rate of the enzyme-catalyzed reaction is measured.
Turnover number, also known as kcat (catalytic constant), is a parameter that describes the efficiency of an enzyme. It represents the number of substrate molecules converted into product per unit time by a single active site of the enzyme when it is fully saturated with substrate. Turnover number is calculated by dividing the enzyme activity by the enzyme concentration.
To measure enzyme activity and determine the turnover number, you can follow these steps:
1. Prepare the enzyme assay: Design your experiment by selecting appropriate substrates, cofactors, and buffers that match the enzyme's optimal conditions. Ensure that all necessary reagents and equipment are ready.
2. Set up the reaction mixture: Combine the enzyme, substrate, and other required components in a reaction tube or cuvette. Maintain the reaction at the desired temperature and pH.
3. Start the reaction: Initiate the reaction by adding the substrate to the enzyme and thoroughly mix the reaction mixture. Ensure that the reaction conditions are well-controlled and consistent throughout the experiment.
4. Time the reaction: Record the elapsed time from the moment the reaction starts. For accurate results, measure the initial velocity of the reaction by monitoring the reaction's progress during the linear portion of the reaction curve.
5. Measure the reaction's product formation: Use appropriate techniques such as spectrophotometry, colorimetry, or fluorometry to quantify the product formed during the reaction. The specific method depends on the nature of the reaction and the nature of the product.
6. Calculate the enzyme activity: Determine the amount of product formed per unit time and per unit enzyme concentration. This will give you the enzyme activity in international units (IU). The formula for calculating enzyme activity is:
Enzyme Activity = (ΔProduct / ΔTime) / Enzyme Concentration
7. Determine the turnover number: Divide the enzyme activity by the enzyme concentration to obtain the turnover number. The formula for calculating turnover number (kcat) is:
Turnover Number (kcat) = Enzyme Activity / Enzyme Concentration
By following these steps, you can measure enzyme activity and determine the turnover number, providing valuable information about the efficiency and catalytic potential of the enzyme.