Enzymology Services
Enzyme Inhibition Kinetics
Resolve how your inhibitor actually works — competitive, uncompetitive, noncompetitive, mixed, or time-dependent — with mechanism-based.
What Inhibition Kinetics Answers
Enzyme inhibition kinetics quantifies how a small molecule modulates catalytic rate by measuring initial velocities across a matrix of substrate and inhibitor concentrations. Rather than reporting a single potency number under fixed conditions, the approach fits the resulting data to inhibition models — competitive, uncompetitive, noncompetitive, or mixed — so that the mechanism of action is defined rather than assumed.
That mechanistic resolution matters because two compounds with similar potency can behave very differently in a biological system. A competitive inhibitor can be overcome by rising substrate concentrations, while a noncompetitive or irreversible inhibitor may not. Kinetic profiling also supports the classification of reversible versus irreversible behavior, and for time-dependent inhibitors it provides the inactivation parameters used to reason about potency and duration of effect.
The service is built for drug discovery teams in pharma and biotech working on enzyme targets, and for academic groups studying enzyme regulation. Programs commonly use these datasets to prioritize compounds during hit-to-lead and lead optimization, to understand PK/PD disconnects, and to build better models of the therapeutic window.
Inhibition Mechanism Assignment
Global fitting across substrate and inhibitor titration series distinguishes competitive, uncompetitive, noncompetitive, and mixed behavior instead of reporting a single fixed-condition number.
- Michaelis-Menten and Lineweaver-Burk analysis of initial-rate data
- Global fitting to candidate inhibition models with model comparison
- Substrate concentration set relative to the measured Km
Ki and kinact/KI Determination
Reversible binders are characterized by their inhibition constant; time-dependent and irreversible inhibitors are characterized by inactivation kinetics that describe potency and duration of effect.
- Ki determination for reversible inhibitors
- Time-dependent inactivation assays for irreversible inhibitors
- kinact/KI determination and IC50 shift with preincubation for TDI
Enzyme Source Flexibility
Assays are configured around the enzyme system that is relevant to your program, from purified and recombinant targets to microsomal preparations used in drug metabolism work.
- Purified enzymes and recombinant CYP or kinase targets
- Human and rat liver microsomes (HLM/RLM)
- Cocktail assay formats for CYP isoform selectivity
Mechanism Classes We Resolve
Each inhibition class produces a distinct kinetic signature, and the experimental design is adjusted accordingly. The table below summarizes how the major classes are typically distinguished and what parameter is reported for each.
Classification is not always clean-cut. Mixed and partial inhibition patterns are common, and time-dependent behavior can be missed if preincubation is not built into the design. Where the data support more than one model, we report the competing fits and the evidence that favors one interpretation over another.
| Inhibition class | Kinetic signature | Primary parameter | Typical design consideration |
|---|---|---|---|
| Competitive | Apparent Km increases with inhibitor; Vmax unchanged | Ki | Substrate range bracketing Km to expose the shift |
| Uncompetitive | Both apparent Km and Vmax decrease | Ki | Higher substrate concentrations needed to populate the ES complex |
| Noncompetitive | Vmax decreases; apparent Km largely unchanged | Ki | Inhibitor titration at fixed, Km-relative substrate levels |
| Mixed | Both apparent Km and Vmax change, in either direction | Ki and Ki' | Global fitting across the full matrix rather than single plots |
| Time-dependent / irreversible | Potency increases with preincubation time | Preincubation series and IC50 shift comparison |
How an Engagement Works
Projects follow a defined sequence from assay configuration through mechanism assignment and reporting. The steps below describe what happens at each stage; the exact scope is agreed with you before work begins.
Target and system scoping
We confirm the enzyme system, substrate, cofactors, detection method, and the decision your program needs to make, then define the substrate and inhibitor concentration ranges that will resolve the mechanism.
Substrate titration for Km and Vmax
A substrate titration establishes Km and Vmax under your chosen conditions, so that subsequent inhibitor experiments can be run at substrate concentrations set relative to the measured Km rather than at arbitrary levels.
Inhibitor titration and initial-rate measurement
Inhibitor titrations are run at fixed substrate concentrations, with velocities measured in the linear phase of the reaction. Replicates and positive controls are included to confirm the assay is behaving as expected.
Mechanism fitting and parameter determination
Velocity data are analyzed by Michaelis-Menten and Lineweaver-Burk treatment and then fitted globally to candidate inhibition models. Reversible inhibitors yield Ki; time-dependent inhibitors are assessed by preincubation series to derive kinact/KI.
Where the Data Gets Used
Kinetic parameters feed directly into the decisions that move a program forward. The three areas below are the most common applications, though the fit to your workflow is discussed during scoping.
Because the same dataset can serve several purposes, we recommend stating the intended use up front — for example, compound ranking versus mechanistic publication — so that replication and control levels match the required confidence.
Lead Selection and Optimization
Kinetic parameters add a mechanistic dimension to structure-activity relationships, helping medicinal chemistry teams distinguish compounds that look similar on potency alone.
- Mechanism-aware ranking within a compound series
- Support for iterative design cycles
- Classification of reversible versus irreversible behavior
PK/PD and Therapeutic Window Reasoning
Inactivation kinetics and mechanism class inform how compound behavior may translate, and help explain apparent disconnects between biochemical potency and cellular or in vivo readouts.
- Time-dependent inhibition assessment by preincubation
- kinact/KI for irreversible and covalent inhibitors
- Context for duration-of-effect discussions
Drug Metabolism and DDI Risk
For drug-metabolizing enzyme targets, inhibition kinetics and cocktail-format assays support assessment of isoform selectivity and the potential for clinically relevant interactions.
- CYP isoform selectivity by cocktail assay
- Human and rat liver microsome formats
- Reversible and time-dependent inhibition characterization
Project Scope Parameters
Scope is defined case by case after a short technical discussion, because the right design depends on your enzyme, your compound class, and the decision the data must support. The table below lists the parameters that are typically agreed before work starts.
Nothing here is a fixed bundle. Substrate ranges, inhibitor concentrations, replication, and the depth of computational follow-up are all set in the project scope of work.
| Parameter | Typical project scope | How it is decided | What you receive |
|---|---|---|---|
| Enzyme system | Purified enzyme, recombinant target, or liver microsomes (HLM/RLM) | Based on target class and intended application | Documented source and assay conditions |
| Substrate range | Titration bracketing the measured Km | Set after the Km determination step | Km and Vmax with fitted curves |
| Inhibitor concentrations | Multi-point titration at fixed substrate levels | Chosen to span the response and support model fitting | Rate data and fitted inhibition parameters |
| Mechanism models tested | Competitive, uncompetitive, noncompetitive, and mixed | Selected from the observed data pattern | Model comparison and assigned mechanism |
| Reversible parameter | Ki determination | Applies when inhibition is reversible | Ki value with confidence interval |
| Time-dependent assessment | Preincubation series and IC50 shift | Included when inhibition increases with preincubation | |
| Selectivity screening | Cocktail assay across CYP isoforms | Scoped when isoform selectivity is a program question | Isoform-level inhibition profile |
| Replication and controls | Replicates plus positive controls and linear-range verification | Set according to the confidence the decision requires | QC summary with the dataset |
Assay Quality Controls
Kinetic parameters are only as reliable as the assay that produced them. Every project includes the controls needed to show that the measured rates reflect enzyme activity rather than assay artifacts.
Where a result is ambiguous — for example, when two inhibition models fit comparably well — we report the ambiguity rather than forcing a single assignment.
Linear-Phase Verification
Initial velocities are measured only within the linear phase of the reaction, so that the rates used for fitting are not distorted by substrate depletion or product inhibition.
- Reaction progress checked before rate determination
- Substrate consumption kept within acceptable limits
- Detection method matched to the enzyme system
Positive Controls and Replicates
Known inhibitors and replicate wells are included to confirm that the assay responds as expected and that the measured effect is reproducible.
- Positive control inhibitor in each run
- Replicate determinations for key conditions
- Consistency checks across plates and days
Model Comparison and Reporting
Data are fitted to multiple candidate models and compared, so the reported mechanism reflects the best-supported interpretation of the full dataset.
- Global fitting rather than single-plot interpretation
- Confidence intervals reported with each parameter
- Underlying rate data provided with the report
Deliverables and Reporting
Deliverables are defined in the project scope of work. The table below shows the categories of output that a typical inhibition kinetics project produces, and what each item is used for.
Raw data are provided alongside the fitted results so that your team can re-analyze or extend the dataset internally if needed.
| Deliverable | Content | Format | Typical use |
|---|---|---|---|
| Kinetic parameter report | Km, Vmax, Ki, and kinact/KI as applicable | Written report with fitted values and confidence intervals | Compound ranking and mechanism assignment |
| Mechanism assignment | Best-supported inhibition model with comparison to alternatives | Narrative section with supporting plots | SAR interpretation and design decisions |
| Raw rate data | Initial velocities across the substrate and inhibitor matrix | Tabulated dataset | Independent re-analysis or model extension |
| QC summary | Positive controls, linear-range checks, and replicate agreement | Summary table | Internal data quality documentation |
| Interpretation notes | What the mechanism implies for the compound series | Written commentary | Project team discussion and next-step planning |
Reversible Versus Irreversible
The distinction between reversible and irreversible inhibition changes both the experimental design and the interpretation of the result. Reversible inhibitors are characterized by an inhibition constant that describes binding equilibrium, while irreversible and time-dependent inhibitors are characterized by inactivation kinetics that describe how quickly the enzyme is inactivated per unit of inhibitor exposure.
A compound that appears to be a simple reversible inhibitor in a short assay can reveal time-dependent behavior once preincubation is introduced. For this reason, projects that involve covalent or slowly binding compounds typically include a preincubation series and an IC50 shift comparison as part of the standard design.
Enzyme Systems and Formats
Inhibition kinetics can be run against a range of enzyme preparations, and the choice of system should reflect the biological question rather than convenience. Purified and recombinant enzymes give the cleanest mechanistic readout, while microsomal preparations capture the more complex behavior relevant to drug metabolism.
For programs concerned with metabolic liability, cocktail-format assays allow several cytochrome P450 isoforms to be interrogated in a single experiment, which is a practical way to assess selectivity across isoforms before committing to a larger study.
FAQ
How is inhibition kinetics different from a standard IC50 measurement?
An IC50 is a single concentration-response value measured under one fixed set of conditions. Inhibition kinetics measures initial velocities across multiple substrate and inhibitor concentrations, which allows the data to be fitted to a mechanism model and yields a Ki or kinact/KI value. The kinetic approach tells you how the compound inhibits, not just how potently it does so under one condition.
Which enzyme systems can be used for these assays?
Projects commonly use purified enzymes, recombinant targets such as CYP or kinase enzymes, and human or rat liver microsomes. The appropriate system depends on your target class and the decision the data needs to support, and it is agreed during project scoping before experiments begin.
How do you determine whether an inhibitor is reversible or irreversible?
Reversibility is assessed by comparing inhibition measured with and without a preincubation step. If potency increases with preincubation time, the compound shows time-dependent behavior and is characterized by inactivation kinetics rather than a simple equilibrium constant. Reversible inhibitors are reported with a Ki value, while time-dependent inhibitors are reported with kinact/KI.
What controls are included to make sure the kinetic data are reliable?
Runs include positive control inhibitors, replicate determinations for key conditions, and verification that initial velocities are measured within the linear phase of the reaction. Substrate concentrations are set relative to the measured Km, and data are fitted globally to candidate models so that the reported mechanism reflects the best-supported interpretation of the full dataset.
Can the same project cover both mechanism assignment and selectivity screening?
Yes. Mechanism assignment and selectivity screening are often combined, for example when a program needs both a Ki for the primary target and an isoform-level inhibition profile from a cocktail assay. The combination is defined in the project scope of work so that the experimental design supports both questions without redundant work.
References
- Mohutsky M, Hall SD. Irreversible Enzyme Inhibition Kinetics and Drug-Drug Interactions. Methods in molecular biology (Clifton, N.J.). 2021;2342:51-88. View on PubMed
- Corrionero A, Zhang X, Alfonso P, et al. An Assessment of Kinase Selectivity, Enzyme Inhibition Kinetics and in Vitro Activity for Several Bruton Tyrosine Kinase (BTK) Inhibitors. ACS pharmacology & translational science. 2025;8(12):4312-4325. View on PubMed
- Panigrahy M, Dua A. Molecular noise-induced activator-inhibitor duality in enzyme inhibition kinetics. The Journal of chemical physics. 2023;159(15). View on PubMed
- Gao J, Zhang Y, Lei X, et al. Risk assessment of the inhibition of hydroxygenkwanin on human and rat cytochrome P450 by cocktail method. Toxicology in vitro: an international journal published in association with BIBRA. 2022;79:105281. View on PubMed
- Mermer A, Demirci S. Recent advances in triazoles as tyrosinase inhibitors. European journal of medicinal chemistry. 2023;259:115655. View on PubMed
- Nagar S, Argikar UA, Tweedie DJ. Enzyme kinetics in drug metabolism: fundamentals and applications. Methods in molecular biology (Clifton, N.J.). 2014;1113:1-6. View on PubMed
Start With a Technical Discussion
Share your target, compound class, and the decision the data needs to support. We will propose a substrate and inhibitor design, confirm the enzyme system, and define the scope of work before any experiments begin.