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Activation of Integrins01:15

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Contact-dependent signaling, as the name suggests, requires that communicating cells be in direct contact with each other. This is achieved either through receptor-ligand interactions or by specialized cytoplasmic channels that allow the flow of small molecules between cells. In animal cells, channels called gap junctions facilitate contact-dependent signaling in certain tissues, whereas, plasmodesmata perform a similar function in plants.
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Related Experiment Video

Updated: Mar 10, 2026

Spatial and Temporal Control of T Cell Activation Using a Photoactivatable Agonist
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New Tools to Study Contact Activation.

Steffen Rosén1

  • 1Private Practice , Molndal , Sweden.

Frontiers in Medicine
|December 7, 2016
PubMed
Summary

Researchers developed sensitive chromogenic assays for FXIIa and kallikrein, adapting a Factor XIa (FXIa) method. These assays, utilizing FXa generation, offer rapid and precise measurements for studying contact factor enzymes and inhibitors.

Area of Science:

  • Biochemistry
  • Enzymology
  • Hemostasis

Background:

  • The determination of activated Factor XI (FXIa) activity has been facilitated by sensitive chromogenic assays.
  • Extending these methods to related contact factor enzymes like Factor XIIa (FXIIa) and kallikrein is of significant interest for hemostasis research.

Purpose of the Study:

  • To adapt and validate a sensitive chromogenic FXIa assay for the determination of FXIIa and kallikrein activities.
  • To assess the utility of these new assays in studying enzyme kinetics and inhibitor interactions.

Main Methods:

  • A chromogenic assay, initially developed for FXIa, was modified for FXIIa and kallikrein using FXa generation as the readout.
  • Enzyme stability and assay performance were evaluated in MES-bovine serum albumin (BSA) buffer at pH 5.7, with and without inhibitors like aprotinin and corn trypsin inhibitor.
Keywords:
FXIIaFXIachromogenickallikreinmethods

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  • Kinetic studies involved subsampling and dilution in the specialized buffer to quench enzyme activity before FXa determination.

    • Main Results:

    • The adapted assays demonstrated sensitivity in the 1-10 nmol/L range, providing approximately 0.8 absorbance units resolution within a 20-minute timeframe.
    • FXIa, FXIIa, and kallikrein exhibited stability for at least 5 hours when stored on ice in MES-BSA buffer.
    • The MES-BSA buffer at pH 5.7 effectively quenched enzyme activity, enabling reliable determination of FXa generation.

    Conclusions:

    • The adapted sensitive chromogenic FXIa assay, particularly with the MES-BSA buffer, presents a valuable new tool for investigating contact factor enzymes and their inhibitors.
    • While promising for purified systems, further research is needed to confirm the applicability of these methods for determining FXIIa and kallikrein activities in plasma samples.