Ever-fluctuating single enzyme molecules: Michaelis-Menten equation revisited

Nat Chem Biol. 2006 Feb;2(2):87-94. doi: 10.1038/nchembio759. Epub 2005 Dec 25.


Enzymes are biological catalysts vital to life processes and have attracted century-long investigation. The classic Michaelis-Menten mechanism provides a highly satisfactory description of catalytic activities for large ensembles of enzyme molecules. Here we tested the Michaelis-Menten equation at the single-molecule level. We monitored long time traces of enzymatic turnovers for individual beta-galactosidase molecules by detecting one fluorescent product at a time. A molecular memory phenomenon arises at high substrate concentrations, characterized by clusters of turnover events separated by periods of low activity. Such memory lasts for decades of timescales ranging from milliseconds to seconds owing to the presence of interconverting conformers with broadly distributed lifetimes. We proved that the Michaelis-Menten equation still holds even for a fluctuating single enzyme, but bears a different microscopic interpretation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Catalysis
  • Galactosides / chemistry
  • Galactosides / metabolism
  • Kinetics
  • Microscopy, Fluorescence
  • Molecular Conformation
  • Oxazines / chemistry
  • Oxazines / metabolism
  • beta-Galactosidase / chemistry*
  • beta-Galactosidase / metabolism


  • Galactosides
  • Oxazines
  • resorufin galactopyranoside
  • beta-Galactosidase

Associated data

  • PubChem-Substance/7980932
  • PubChem-Substance/7980933