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Harold B. Brooks coauthored practical guidance for designing enzyme assays used to test many candidate compounds. His 2012 chapter explains how enzyme kinetics, the choice of reaction substrate and controls determine whether an assay can identify reversible enzyme inhibition. Its emphasis on initial rates connects an instrument's signal to a defined biochemical reaction rather than treating an endpoint measurement as self-explanatory.^[ref]

For example, imagine an enzyme assay that starts with $100$ micromolar reaction substrate. Measuring after only $5$ micromolar has been consumed leaves its concentration approximately unchanged; measuring after $80$ micromolar has been consumed does not. The chapter recommends establishing an early linear interval with little substrate depletion, checking several enzyme concentrations and measuring background signals with appropriate missing-component controls. A later plateau can reflect exhausted reaction substrate rather than loss of enzyme activity. This is why an enzyme inhibition initial-rate assay needs a time course before it can turn a smaller signal into evidence about inhibition.^[ref]