The simultaneous collapse of both the swinging crossbridge theory of muscle contraction and the in vitro motility essays.
In the early seventies we discovered that isolated, active, myosin fragments can induce movement and tension generation by actin filaments in both in vitro and in vivo systems, employing a variety of techniques. It was not in line with the domineering swinging crossbridge theory of muscle contraction. We then proposed an hydrodynamic mechanism which explained our results and was applied to muscle contraction and to other biological engines. Our discovery has been ignored for a long time until the so-called "in vitro motility essays" appeared. By using this artifact--laden technique the mechanochemical reactivity of the active myosin fragments was re-discovered without giving us any credit. The essays gave continuously changing values for fundamental parameters of muscle contraction; the values were appreciably different in different laboratories and decreased in a continuous fashion in the hands of one scientist. By analyzing recent experiments which derived the rate of ATP hydrolysis of active muscles as function of the applied load I calculated the value of the sliding distance resulting from the breakdown of one ATP molecule by each of the myosin heads in contracting muscle. According to the contemporary theory this should be the same for all muscles under any environmental conditions and determined by length of the myosin head's neck. My examination led to the conclusion that the sliding distance varies from one muscle to another and with different temperatures for the same muscle. This again, contradicts the current theory and should give the final blow to both this theory and the "essays". Furthermore: it can be explained by a hydrodynamic mechanism such as that proposed by us more than 30 years ago.
Oplatka
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Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel. avraham.oplatka@weizmann.ac.il
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D009218:Myosins / Q000378:metabolism
D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins