The Ultra-Sensitive AptaFluor® SAH Methyltransferase Assay

The AptaFluor SAH Methyltransferase Assay uses a highly sensitive RNA aptamer that is capable of directly detecting SAH. The sensitivity of the aptamer (measures SAH at concentrations below 10 nM), allows detection of methyltransferase activity at physiological concentrations of SAM. The unique direct detection format simplifies the protocol (no coupling enzyme needed) and minimizes compound interference.

Because the assay is based on direct SAH detection, it is well-suited for SAM-dependent methyltransferases that are representive of typical low K(100 nM to 5 µM). It is an easy-to-use and HTS-ready assay designed for screening and profiling inhibitors. The assay can be used to:

  • Measure the enzymatic activity of methyltransferases
  • Screen compound libraries for modulators
  • Quantify inhibitor potency
  • Inhibitor selectivity profiling

Image Credit: BellBrook Labs

Methyltransferase Target Applications

The table below includes example methyltransferase enzymes we have validated with the AptaFluor SAH Assay. Click on a target to learn more. 

Methyltransferase Enzyme

Source: BellBrook Labs

Why Choose AptaFluor?

  • Use SAM concentrations as low as 100 nM and as high as 5 μM
  • Direct detection of SAH
  • Easy to use, two-step format (no coupling enzymes needed)
  • Robust Assay Z’ > 0.7 under initial velocity conditions
  • Far-red fluorescent readouts reduce compound interference
  • A non-radioactive, safe technique

Example Data Using MLL4 MTase

Robust Assay Ready to Scale


Z' = 0.72. Robust data is neccessary to confirm the assay is well-suited for screening large compound libraries in a high-throughput format. 

Image Credit: BellBrook Labs

Detecting SAH Under Initial Velocity Conditions

MLL4 Titration

MLL4 enzyme titration using AptaFluor SAH Assay with TR-FRET readout. The enzyme reaction components included 10 μM Histone H3 substrate, 350 nM SAM, 50 mM Tris-HCl (pH 8.6), 2 mM MgCl2, 0.02% Triton X-100, and 1 mM DTT. The Enzyme Stop Mix included 1X Enzyme Stop Reagent and 1X SAH Detection Buffer. The SAH Detection Mix consisted of 20 nM P1-Terbium Mix, 40 nM P2-Dylight 650 nM, and 1X SAH Detection Buffer. 

Image Credit: BellBrook Labs

Mll4 Linear Response

MLL4 linear response. The assay shows linearity when raw data is converted to SAH using a standard curve. 

Image Credit: BellBrook Labs

Lead Discovery Services

BellBrook Labs also offers lead discovery services for scientists who want to advance their program but don't want to bring a biochemical assay in-house. Their services feature customizable assay conditions, quick turnaround times, and direct collaboration with a BellBrook scientist. Lead discovery services can include:

  • Inhibitor Screening
  • Inhibitor Potency Profiling
  • Inhibitor Selectivity Profiling
  • Residence Time Measurements
  • Mechanism of Action Studies
  • Triage Non-Stoichiometric Inhibitors
  • Compound-Target Binding with Thermal Shift Assays 

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