Prof. Klafter Joseph (Yossi)

Affiliation:School of chemistry
Ornstein building
room 209
Tel:  (972)-3-6408254
Fax: (972)-3-6406466
Personal Website:

Postal Address:School of chemistry
Tel Aviv University
Tel Aviv 69978

Research Interest

Biological Processes on the Level of a Single Molecule

Single molecule techniques offer a unique tool to study in real-time the dynamical behaviour of individual molecules and provide the possibility to construct distributions from individual events rather than from a signal stemming from an ensemble of molecules. In biological systems, known for their complexity, these techniques make it possible to gain insights into the detailed spectrum of molecular conformational changes and activities. In collaboration with experimental groups in Europe we observed a single enzyme reaction for extended periods of time (hours), using confocal fluorescence microscopy. When adding a profluorescent substrate the monitored enzymatic activity appeared as a trajectory of on-state and off-state events.  The waiting time probability density function (PDF) of the off-state and the state-correlation function fit stretched exponentials, independent of the substrate concentration in a certain range. In addition, clusters of fast events were detected in the ordered off waiting times trajectory, indicating correlations in the activity. Our findings imply that a fluctuating enzyme model, which involves a spectrum of enzymatic conformations that interconvert on the timescale of the catalytic activity, best describes the observed enzymatic activity. The “text book” Michaelis–Menten  scheme has been modified accordingly.

Selected Publications

  • O. Flomenbom, K. Velonia, D. Loos, S. Masuo, M. Cotlet, Y. Engelborghs, Hofkens, A.E. Rowan, R.J.M. Nolte, F.C. de Schryver and J. KlafterTemporal Stretched Exponential Decay and Correlations in the Catalytic behavior of Fluctuating Individual Lipase MoleculesProc. Nat. Acad. Sci. (USA), 102, 2368-2372 (2005).
  • K. Velonia, O. Flomenbom, D. Loos, S. Masuo, M. Cotlet, Y. Engelborghs, Hofkens, A.E. Rowan, J. Klafter, R.J. M. Nolte and F.C. de SchryverSingle Enzyme Kinetics of CALB Catalyzed HydrolysisAngewandte Chemie 44, 560-564 (2005). Front cover
  • O. Flomenbom, J. Klafter and A. SzaboWhat Can One Learn from Two-State Single Molecule TrajectoriesBiophys. J. 88, 3780-3783 (2005).