Structure and paramyosin content of tarantula thick filaments.
- 1 July 1983
- journal article
- research article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 97 (1), 186-195
- https://doi.org/10.1083/jcb.97.1.186
Abstract
Muscle fibers of the tarantula femur exhibit structural and biochemical characteristics similar to those of other long-sarcomere invertebrate muscles, having long A-bands and long thick filaments. Thin filaments (9-12) surround each thick filament. Tarantula muscle has a paramyosin:myosin H chain molecular ratio of 0.31 .+-. 0.079 SD. The myosin cross-bridge arrangement on the surface of tarantula thick filaments on isolated, negatively stained, and unidirectionally metal-shadowed specimens were studied by EM and optical diffraction and filtering and was similar to that previously described for the thick filaments of muscle of the closely related chelicerate arthropod, Limulus. Cross-bridges are disposed in a 4-stranded right-handed helical arrangement, with 14.5-nm axial spacing between successive levels of 4 bridges and a helical repeat period every 43.5 nm. The orientation of cross-bridges on the surface of tarantula filaments is also likely to be very similar to that on Limulus filaments as suggested by the similarity between filtered images of the 2 types of filaments and the radial distance of the centers of mass of the cross-bridges from the surfaces of both types of filaments. Tarantula filaments have smaller diameters than Limulus filaments, contain less paramyosin, and display structure that probably reflects the organization of the filament backbone which is not as apparent in images of Limulus filaments. The similarities between Limulus and tarantula thick filaments may be governed, in part, by the close evolutionary relationship of the 2 species.This publication has 29 references indexed in Scilit:
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