Table 1.
Key Kinetic Values for the Discussion of Enzyme-Targeted Molecular Imaging Agents.
| Kinetic Value | Type | Definition |
|---|---|---|
| IC50 | Binding measure | Concentration of substrate at which enzyme activity is reduced by 50% under given assay conditions |
| V max | Maximum rate | Maximum rate of enzyme reaction |
| Ki , reversible | Inhibition constant | Equilibrium constant for binding of the inhibitor, ratio of the rate constant for enzyme–inhibitor dissociation divided by the ratio of enzyme–inhibitor association (koff/kon) |
| Ki , irreversible | Inhibition constant | Concentration at which the inactivation reaction proceeds at 50% of the maximum velocity (analogous to Km for a substrate) |
| ki | Rate | Rate constant for the reaction that generates the inactivated form of the enzyme (EI*) once the enzyme is saturated by the irreversible inhibitor (analogous to kcat for a substrate) |
| Km | Michaelis constant | Concentration of substrate needed to reach half the maximum rate (V max) |
| kcat | Rate | Rate of the first committed chemical step of the reaction at saturating substrate concentrations |
| kon | Rate | Rate of substrate binding to enzyme active site |
| koff | Rate | Rate of substrate dissociating from enzyme active site |