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Published 29 September 2003. doi:10.1083/jcb.200304006
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© The Rockefeller University Press, 0021-9525/2003/9/1183 $8.00
The Journal of Cell Biology, Volume 162, Number 7, 1183-1188

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Stored elastic energy powers the 60-µm extension of the Limulus polyphemus sperm actin bundle



Jennifer H. Shin1, L. Mahadevan4, Guillermina S. Waller5, Knut Langsetmo6 and Paul Matsudaira2,3,5

1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
2 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
3 Division of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
4 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, CB3 9EW, Cambridge, UK
5 Whitehead Institute for Biomedical Research, Cambridge, MA 02142
6 Boston Biomedical Research Institute, Watertown, MA 02472

Address correspondence to L. Mahadevan, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, CB3 0WA, Cambridge, UK. Tel.: 44-1223-766-891. Fax: 44-1223-765-900. email: l.mahadevan{at}damtp.cam.ac.uk

During the 5 s of the acrosome reaction of Limulus polyphemus sperm, a 60-µm-long bundle of scruin-decorated actin filaments straightens from a coiled conformation and extends from the cell. To identify the motive force for this movement, we examined the possible sources of chemical and mechanical energy and show that the coil releases ~10-13 J of stored mechanical strain energy, whereas chemical energy derived from calcium binding is ~10-15 J. These measurements indicate that the coiled actin bundle extends by a spring-based mechanism, which is distinctly different from the better known polymerization or myosin-driven processes, and that calcium initiates but does not power the reaction.

Key Words: acrosomal reaction; mechanical spring; calcium energy; calorimetry

The online version of this article includes supplemental material.

Abbreviations used in this paper: FD, false discharge; TD, true discharge.


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