| Label | EC50c | Emaxc | Basalc | EC50m | Emaxm | Basalm | α | β | AMI (wP=0.5, wE=0.5, ln) |
|---|---|---|---|---|---|---|---|---|---|
| PAM example | 100 nM | 80 | 0 | 25 nM | 95 | 0 | 4.0000 | 1.1875 | 77.90 |
| NAM example | 100 nM | 80 | 0 | 200 nM | 60 | 0 | 0.5000 | 0.7500 | -49.05 |
| Neutral example | 100 nM | 80 | 0 | 95 nM | 79 | 0 | 1.0526 | 0.9875 | 1.62 |
α = EC50_control / EC50_modulatedβ = (Emax_mod − Basal_mod) / (Emax_ctrl − Basal_ctrl)AMI = 100 × ( wP × log(α) + wE × log(β) )wP + wE = 1. Use ln or log10 consistently.
Occ = [B]/([B]+KB) and AMI_norm = AMI / Occ.
- Fit dose–response curves for control and modulated conditions to obtain EC50 and Emax.
- Enter EC50 values with units and keep response scales consistent.
- Provide Basal if your assay has a non-zero baseline response.
- Choose weights to emphasize potency vs efficacy for your project.
- Click Calculate to view AMI, classification, and supporting factors.
- Use CSV/PDF buttons to export results for lab notes or reporting.
Purpose of an Allosteric Modulation Index
Allosteric modulators shift agonist curves without acting as orthosteric agonists, so side-by-side interpretation benefits from a standard score. This tool converts fitted potency and efficacy changes into a single, unitless Allosteric Modulation Index (AMI) for ranking compounds, tracking SAR, and summarizing assay impact across runs when fitting and scaling are consistent. Scaled by 100, AMI stays readable when fold-changes are modest in screening.
Potency Shift Data (EC50) and Unit Handling
Potency modulation is captured as α = EC50control / EC50modulated. Lowering EC50 from 100 nM to 25 nM gives α = 4.0, a four-fold potency gain.
Units (M to fM) are converted internally, but both EC50 values must be positive and derived from the same curve model, constraints, and response normalization.
If EC50 increases from 100 to 200 nM, α becomes 0.5, indicating reduced potency.
Efficacy Shift Data (Emax and Basal)
Efficacy modulation uses β = (Emaxmod − Basalmod)/(Emaxctrl − Basalctrl), focusing on net signal above baseline.
This helps when background is non-zero or baseline differs between conditions. If control net response is 80 and modulated is 95, β = 1.1875.
Enter Basal only when measured on the same scale as Emax. Avoid denominators near zero; unstable β usually signals poor assay window or fit.
Weighting, Log Choice, and Normalization
AMI combines both terms: AMI = 100 × (wP × log(α) + wE × log(β)), with weights normalized so wP + wE = 1.
Increase wP when EC50 improvement drives decisions, or increase wE when maximal response is critical.
Choose ln or log10 and keep it consistent for comparisons. Optional occupancy uses Occ = [B]/([B]+KB) to report AMI/Occ for dose-adjusted benchmarking.
The tool rescales weights automatically, so any positive pair is acceptable.
Interpreting Results and Reporting Outputs
Positive AMI is PAM-like, negative AMI is NAM-like, and values near zero indicate weak or mixed effects. Set thresholds to match assay variability (for example, ±5 for low noise). Export CSV for downstream analysis and PDF for reporting, or paste multiple rows in batch mode to screen libraries quickly with the same settings. Use α×β as a fold summary before deeper mechanistic review.
A positive AMI indicates overall positive modulation, typically consistent with PAM-like behavior. It reflects increased potency (α>1), increased efficacy (β>1), or both, depending on your chosen weights.
Log transforms turn fold-changes into additive terms, so a 4× potency gain and a 0.5× loss are symmetric in magnitude. This makes AMI more stable for ranking across wide dynamic ranges.
Enter Basal when your assay has a measurable baseline signal on the same scale as Emax. If baseline is unknown or already subtracted during normalization, keep Basal at zero for both conditions.
Start with 0.5/0.5 for balanced ranking. Increase wP when EC50 improvement is your key endpoint, or increase wE when changes in maximal response drive efficacy, safety margins, or functional selectivity decisions.
If you provide modulator concentration and KB, the calculator estimates occupancy and reports AMI/Occ. This helps compare modulation strength at different concentrations by scaling the observed effect to receptor engagement.
You can, if EC50 and Emax are fitted consistently and the response scale is comparable. If assay windows differ, consider using Basal inputs and consistent normalization, and interpret thresholds within each platform.