The micromechanics of contraction.
This paper suggests the molecular mechanism in muscle whereby some of the delta G of ATP hydrolysis is converted to mechanical work. There is good evidence for thinking that all mechanical, thermal, and chemical observations of muscle result from the summated, repetitive, operation of identical unitary "engines". Such an engine is the S-1 moiety of a myosin crossbridge and the adjacent actin. The operational principle is evident on realizing that S-1 is a particle with two interactive ligand (ATP and actin) binding sites. The change resulting from binding nucleotide is propagated to the actin-binding site, there specifying affinity and angles of attachment. Repetition follows because stepwise enzymatic degradation through intermediates is equivalent to cyclical changing of the site occupant. Trans- (S-1) propagation ensures a work cycle because actin held at a succession of relative positions can generate external work. Proximity mapping and protein chemical studies of S-1 suggest that variation in the position at which actin is held results from the simultaneous operation of a continuing (S-1)-actin contact and a polyphosphate charge-modulated coulombic contact.
Morales
M F
MF
Cardiovascular Research Institute, University of California, San Francisco 94143.
D000199:Actins / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000502:physiology; D000818:Animals; D001696:Biomechanical Phenomena; D008954:Models, Biological; D009119:Muscle Contraction; D009218:Myosins / Q000502:physiology
D000199:Actins; D000251:Adenosine Triphosphatases; D009218:Myosins