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Cyclic-FMN Is a Detectable, Putative Intermediate of FAD Metabolism

Luxene Belfleur1, Juha P Kallio2, Wito Richter3

  • 1Mitchell Cancer Institute, Mass Spectrometry Core Facility, University of South Alabama, Mobile, AL 36604, USA.

Biomolecules
|January 28, 2026
PubMed

Insights

Researchers synthesized 4

Area of Science:

  • Biochemistry
  • Analytical Chemistry

Background:

  • Free flavin adenine dinucleotide (FAD) metabolism yields flavin mononucleotide (FMN) and adenine monophosphate (AMP).
  • Triose kinase FMN cyclase (TKFC) converts FAD to 4',5'-cyclic phosphoriboflavin (cFMN) and AMP.
  • Underreporting of cFMN incidence in biological samples may stem from a lack of analytical standards.

Purpose of the Study:

  • To synthesize cFMN to establish it as an analytical standard.
  • To optimize reaction conditions for efficient cFMN synthesis from FAD.
  • To characterize the stability and extraction properties of cFMN for biological sample analysis.

Main Methods:

  • Synthesis of cFMN from FMN or FAD.
  • Optimization of FAD to cFMN conversion using ZnSO4.
  • Analysis of cFMN stability under varying pH conditions.
  • Extraction of cFMN from biological samples for LC-MS detection.

Main Results:

  • Optimized reaction conditions using an equimolar ratio of ZnSO4 and FAD yielded pure cFMN.
  • AMP-Zn salts precipitated, facilitating cFMN purification.
  • cFMN demonstrated stability in acidic and basic aqueous conditions.
  • cFMN is readily extracted from biological matrices.
  • Hydrolysis of cFMN to FMN and riboflavin by liver extracts was observed, but mechanisms remain unclear.

Conclusions:

  • A reliable method for synthesizing pure cFMN was established.
  • The developed method enables accurate quantification of cFMN in biological samples.
  • Further research is needed to elucidate the enzymatic pathways of cFMN hydrolysis in liver tissue.
Keywords:
FADcyclic nucleotidecyclic-FMNdivalent cationsriboflavinvitamin B2

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