Which set of techniques is commonly used to measure enzyme activity?

• A. Radiolabeled substrates are the only method to measure enzyme activity.
• B. Fluorometry cannot be used to measure enzyme activity.
• C. Spectrophotometry, fluorometry, and radiolabeling are all used to measure enzyme activity.
• D. Gel electrophoresis directly measures enzyme activity.

Answer: (C)

Measuring enzyme activity relies on detecting a change the enzyme makes, such as converting substrate to product or consuming substrate, and there are several standard formats used to quantify that change. Spectrophotometry is common because many reactions affect absorbance either directly (through a colored product) or indirectly via a coupled reaction that yields a color change. Fluorometry offers high sensitivity when the reaction produces or reveals a fluorescent signal, allowing detection of very small amounts of activity. Radiolabeling uses substrates labeled with a radioactive isotope to track incorporation or release of material with great sensitivity and specificity.

Gel electrophoresis, by itself, separates proteins rather than measuring how fast they catalyze a reaction. It’s not a direct readout of activity unless you use a specialized follow-up method like a zymography assay, which is a distinct technique. That’s why the combination of spectrophotometry, fluorometry, and radiolabeling is commonly used to assess enzyme activity.