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Proceedings of the Royal Society B: Biological Sciences logoLink to Proceedings of the Royal Society B: Biological Sciences
. 2000 Feb 22;267(1441):415–421. doi: 10.1098/rspb.2000.1016

Myosin monomer density and exchange in synthetic thick filaments investigated using fluorescence microscopy with single molecule sensitivity.

P B Conibear 1, C R Bagshaw 1
PMCID: PMC1690533  PMID: 10722224

Abstract

The number of myosin molecules in synthetic thick filaments, prepared by dialysis at 0.12 M NaCl and pH 7.0, was estimated to be between 400 and 800 molecules per micrometre under conditions appropriate for in vitro motility assays. This estimate was based on a number count of Cy3-labelled myosin molecules incorporated into filaments at a nominal ratio of 1:1000. At this dilution, single fluorescent spots were resolved corresponding to individual labelled myosins. The spots usually bleached with a one- or two-step profile but, in around 30% of the cases, fluctuations were observed indicating that additional photophysical or photochemical events had occurred. Myosin molecules were shown to exchange between filaments in suspension on a time-scale of several hours at 4 degrees C, but the reaction was only 75% complete after 48 h, suggesting a non-exchangeable core. However, myosin exchange does not appear to be the predominant source of the fluctuations in fluorescence intensity in the single molecule assays.

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Selected References

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