Affiliation:
1. Randall Centre, King'sCollege London, Guy'sCampus, London SE1 1UL, UK
Abstract
In most current models of muscle contraction there are two translational steps, the working stroke, whereby an attached myosin cross–bridge moves relative to the actin filament, and the repriming step, in which the cross–bridge returns to its original orientation. The development of single molecule methods has allowed a more detailed investigation of the relationship of these mechanical steps to the underlying
biochemistry. In the normal adenosine triphosphate cycle, myosin·adenosine diphosphate·phosphate (M·ADP·P
i
) binds to actin and moves it by
ca
. 5 nm on average before the formation of the end product,
the rigor actomyosin state. All the other product–like intermediate states tested were found to give no net movement indicating that M·ADP·P
i
alone binds in a pre–force state.Myosin states with bound, unhydrolysed nucleoside triphosphates also give no net movement, indicating that these must also bind in a post–force conformation and that the repriming, post– to pre–transition during the forward cycle must take place while the myosin is dissociated from actin. These observations fit in well with the structural model in which the working stroke is aligned to the opening of the switch 2 element of the ATPase site.
Subject
General Agricultural and Biological Sciences,General Biochemistry, Genetics and Molecular Biology
Reference2 articles.
1. Burton K. White H. & Sleep J. 2004 Muscle fibre and actomyosin kinetics using a series of metal-nucleotide substrates. J. Physiol. (In the press.)
2. The Rate of Release of ATP from Its Complex with Myosin
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