Arrangement of myosin heads on Limulus thick filaments.
The two myosin heads with a single surface subunit on thick filaments from chelicerate arthropod muscle may originate from the same, or from axially sequential molecules, as suggested by three-dimensional reconstructions. The resolution attained in the reconstructions, however, does not permit one to distinguish unequivocally between these two possible arrangements. We examined the effect of 0.6 M KCl on relaxed thick filaments separated from Limulus muscle and filaments in which nearest myosin heads were cross-linked by the bifunctional agent, 3,3'-dithio-bis[3'(2')-O-[6-propionylamino)hexanoyl]adenosine 5'-triphosphate (bis22ATP), in the presence of vanadate (Vi). In high salt, surface myosin dissolved from both native, relaxed filaments and those exposed to 1-2 mM dithiothreitol after cross-linking, but was retained on filaments with cross-linked heads. Since bis22ATP must form intermolecular bonds between myosin heads within each subunit to prevent myosin solubilization in high salt, we conclude that each of these heads originates from a different myosin molecule, as was previously predicted by the reconstructions.
Levine
R J
RJ
Department of Anatomy, The Medical College of Pennsylvania, Philadelphia 19129.
Chantler
P D
PD
Kensler
R W
RW
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D003432:Cross-Linking Reagents; D006737:Horseshoe Crabs / Q000648:ultrastructure*; D008958:Models, Molecular; D009132:Muscles / Q000187:drug effects / Q000648:ultrastructure; D009218:Myosins / Q000378:metabolism / Q000648:ultrastructure*; D011189:Potassium Chloride / Q000494:pharmacology; D011487:Protein Conformation; D014638:Vanadates / Q000494:pharmacology
D003432:Cross-Linking Reagents; C050971:3,3'-dithiobis(3'-O-6-(propionylamino)hexanoyl)adenosine 5'-triphosphate; D014638:Vanadates; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D009218:Myosins