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PhosphoSens-Kinetic Enzyme Activity Assays

PhosphoSens-Kinetic assays directly quantify catalytic activity of kinase or phosphatase targets using continuous real-time measurement of substrate phosphorylation or dephosphorylation.

Every well delivers a complete progress curve — simple, add-and-read workflow with high-fidelity kinetic data for more confident decision-making.

How It Works

Assay Principle & Workflow

PhosphoSens assays leverages AssayQuant’s Proprietary Detection Technology to provide real-time, continuous measurements of kinase activity by directly detecting substrate phosphorylation throughout the kinase reaction.

Sensor Peptide Substrates are developed with the Sox readout molecule, covalently attached via a cysteine residue in close proximity to the phosphorylation site (± 2-5 residues). 

As the kinase acts on the substrate, phosphorylation induces a chelation‑enhanced fluorescence (ChEF) signal proportional to phosphorylation level.

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Features & Benefits

Revolutionizing Kinase Research and Drug Development with Continuous Activity Assays

Continuous, Real-Time Monitoring

Directly observe catalytic activity throughout the reaction — no quench steps, no lag-phase ambiguity, and no reliance on artifacts from single-timepoint reads.

TDI-Endpoint-vs-Continuous

Streamlined, Homogeneous Workflow

Add reagents → Read continuously. No wash steps, coupling reactions, or specialized detection equipment needed.

Reproducible, High-Quality Data

Continuous curves reduce variability and improve statistical power for hit validation, SAR, and mechanistic characterization.

Physiologically Relevant Conditions

Peptide substrates derived from biologically relevant sequences. Compatible with low to physiological [mM] concentrations of ATP and native co-factors.

Direct Measurement of Enzyme Activity

Phosphorylation or dephosphorylation of the Sensor Peptide generates the fluorescent signal. No antibodies or secondary enzymes needed.

What Continuous Profiling Reveals That Endpoints Miss

AssayQuant’s Quartet: Same Endpoint, Different Story

In a comparative example, four kinases — TTBK1, FGFR3, BTK, and HCK — each appeared to show ~60–65% inhibition in a standard endpoint assay.
Each mechanism produces similar endpoint values — yet radically different kinetics and implications for inhibitor optimization.

On paper, they look the same, but continuous progress curves tell a very different story:

Target % Inhibition
TTBK1 65%
FGFR3 61%
BTK 61%
HCK 60%
+ or - inhibitor
5mM TTBK1 AC Poster
TTBK1 — Linear, predictable kinetics

This is what you expect a clean enzymatic reaction to look like.
Continuous data confirm stable kinetics and reliable rate determination — with 60+ timepoints per replicate instead of one.

 

3mM FGFR3 AC Poster
FGFR3 — Noisy data reveal solubility artifacts

The continuous trace exposes experimental noise likely caused by compound insolubility — something a single endpoint could never flag.
Detecting such issues early prevents false conclusions and wasted follow-up.

1mM BTK AC Poster
BTK — Saturation & time-dependent inhibition

The curve flattens over time, revealing possible substrate depletion, product inhibition, or slow off-rate behavior.
Early detection of time-dependent inhibition (TDI) provides key clues to mechanism of action (MOA) and compound reversibility.

2nM HCK AC Poster
HCK — Lag phase indicates mechanistic nuance

The lag before steady-state activity hints at conformational effects — for example, the inhibitor preferring an inactive or oligomeric kinase form.
These kinetic patterns are invisible to endpoint assays but critical for mechanistic discovery.

Distinguishing Kinetic from Lysate Mode

PhosphoSens-Kinetic = Recombinant Enzyme Format

Designed for purified recombinant kinases and phosphatases, enabling precise enzymology and inhibitor characterization.

PhosphoSens-Lysate = Endogenous Activity Format

PhosphoSens-Lysate adapts the Kinetic detection principle to measure activity in complex biological samples.

Explore PhosphoSens-Lysate Technology →

Browse Recombinant Enzyme Assay Catalogs

Products > Recombinant Kinase Assays

Browse Our Catalog Of 500+ Protein Kinase Activity Assays To Find The Right PhosphoSens Products For Your Experiments

Products > Recombinant Phosphatase Assays

Explore Our Catalog Of 35+ Protein Phosphatase Activity Assays And Discover Your Next Phosphatase Assay Technology

Resources & Protocols

Understand How Our Technology Can Support Your Next Discovery

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