• Dr. Holger Schmitz
  • Thomas-Mann-Str. 17
  • 51429 Bergisch Gladbach
  • Germany
  • phone: +49 2204 984442
  • HSchm5@freenet.de

I was a post-doc in this lab from 1993-1997. Insect flight muscle is one of the best ordered muscles in nature, a fact that makes it an ideal specimen for studying the structure of crossbridges in different states. By crossbridges, we mean the enzymatic heads of the protein myosin which acts as a “motor” molecule to produce force during muscle contraction. We have been studying the structure of these crossbridges in different biochemical states that can be produced using non-hydrolyzable nucleotide analogs such as AMPPNP. Myosin cannot cleave AMPPNP to produce energy during contraction. However, addtion of AMPPNP to a rigor buffer in which striated muscle fibers are suspended will cause a decrease in the affintiy of myosin for actin. This change mimics the effect of ATP in contracting muscle which causes detachment of crossbridges at the end of the power stroke. We are investigating this effect using electron tomography to obtain 3-D images of the crossbridges. The picture shown at the right illustrates the effect of adding AMPPNP in concert with ethylene glycol on the strtucture. The crossbridges change in both attachment angle and redistribute to different actin binding sites. Specific markers on the thin filament allow us to determine which crossbridges are binding to actin specifically, in which position they could become force bearing crossbridges if the nucleotide was withdrawn, and which attach non-specifically, in which position they must detach and later reattach to a different site on actin in order to become force bearing. These crossbridges that bind actin specifically we call target zone crossbridges. These reconstructions have allowed to verify for the first time that myosin crossbridges can attach to actin in an angle other than the rigor angle.


  • H. Schmitz, C. Lucaveche, M. K. Reedy ; K. A. Taylor. Oblique section 3-D reconstruction of relaxed insect flight muscle reveals the crossbridge lattice in helical registration. Biophys. J. 67, 1620-1633 (1994).
  • H. Schmitz, Mary C. Reedy, Michael K. Reedy, Richard T. Tregear, Hanspeter Winkler, Kenneth A. Taylor. Electron tomography of Insect Flight Muscle in Rigor and AMPPNP at 23oC. J. Mol. Biol. 264, 279-301 (1996).
  • H. Schmitz, M. C. Reedy, M. K. Reedy, R. T. Tregear, H. Winkler, K. A. Taylor. Tomographic 3-D Reconstruction of Insect Flight Muscle Partially Relaxed by AMPPNP and Ethylene Glycol. J. Cell Biol. 139(3), 695-707 (1997).
  • Kenneth A. Taylor, Holger Schmitz, Mary C. Reedy, Yale E. Goldman, Clara Franzini-Armstrong, Hiro Sasaki, Richard T. Tregear, Kate Poole, Carmen Lucaveche, Robert J. Edwards, Li Fan Chen, Hanspeter Winkler, and Michael K. Reedy. Tomographic 3-D reconstruction of quick frozen, Ca++-activated contracting insect flight muscle. Cell 99, 421-431 (1999).
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