Which statement best describes a nonkinetic enzyme assay?

A nonkinetic enzyme assay is characterized by measuring the change in absorbance at specific time points rather than continuously throughout the reaction. The option that states that initial absorbance is measured followed by a second reading after 5 minutes aligns with this definition. This approach enables the determination of enzyme activity by observing the change in absorbance over a defined interval, allowing researchers to assess the reaction without needing continuous monitoring.

In contrast, monitoring absorbance at 10-second intervals or continuously for a minute involves kinetic measurements, where the focus is on the rate of the enzymatic reaction over time. These methods require a more detailed assessment of the enzyme's activity, typically associated with kinetic assays. Measuring reflectance from a pulsed xenon source also deviates from the principle of nonkinetic assays, as it implies a dynamic measurement approach rather than a fixed interval assessment.