Enzyme Kinetics
Read rate curves and distinguish saturation, inhibition, and changes in enzyme activity.
What to do when the question looks unfamiliar
- Step 1Read the axes: product over time or initial rate versus substrate?
- Step 2Compare slopes or plateaus under matched conditions.
- Step 3Make a mechanism claim only as specific as the evidence allows.
Find the rate, then explain a plateau
For product versus time, rate is the slope: change in product divided by change in time. Initial slopes let you compare conditions before substrate depletion or product buildup changes the rate.
For initial rate versus substrate concentration, a plateau at high substrate is consistent with enzyme saturation. More substrate has little effect when the available enzyme is working near its maximum rate. Increasing active enzyme can raise that ceiling.
Use substrate to test an inhibitor explanation
A simple reversible competitive inhibitor reduces rate at lower substrate but can be outcompeted at high substrate, so the same maximum rate is approached. A reduced plateau suggests reduced catalytic capacity, but does not identify a binding site by itself.
Temperature and pH can affect binding, catalytic activity, and protein structure. Activity returning when conditions are restored supports a reversible effect. Hold other variables constant and include a no-inhibitor or vehicle control.