title: Structure and nucleotide-dependent changes of thick filaments in relaxed and rigor plaice fin muscle.
abstract: The myosin crossbridge array, positions of non-crossbridge densities on the backbone, and the A-band "end filaments" have been compared in chemically skinned, unfixed, uncryoprotected relaxed, and rigor plaice fin muscles using the freeze-fracture, deep-etch, rotary-shadowing technique. The images provide a direct demonstration of the helical packing of the myosin heads in situ in relaxed muscle and show rearrangements of the myosin heads, and possibly of other myosin filament proteins, when the heads lose ATP on going into rigor. In the H-zone these changes are consistent with crossbridge changes previously shown by others using freeze-substitution. In addition, new evidence is presented of protein rearrangements in the M-region (bare zone), associated with the transition from the relaxed to the rigor state, including a 27-nm increase in the apparent width of the M-region. This is interpreted as being mostly due to loss or rearrangement of a nonmyosin (M9) protein component at the M-region edge. The structure and titin periodicity of the end-filaments are described, as are suggestions of titin structure on the myosin filament backbone.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269-2242, USA. cantino@uconnvm.uconn.edu
authors.forename: M E
authors.initials: ME
authors.lastname: Cantino
authors.forename: M W K
authors.initials: MW
authors.lastname: Chew
authors.forename: P K
authors.initials: PK
authors.lastname: Luther
authors.forename: E
authors.initials: E
authors.lastname: Morris
authors.forename: J M
authors.initials: JM
authors.lastname: Squire
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D064211:Connectin; D005399:Fishes; D005583:Fourier Analysis; D005614:Freeze Fracturing; D009124:Muscle Proteins / Q000737:chemistry / Q000502:physiology; D009132:Muscles / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure*; D009218:Myosins / Q000737:chemistry* / Q000502:physiology*; D011494:Protein Kinases / Q000737:chemistry / Q000502:physiology
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D009218:Myosins