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Abstract

This chapter describes the analysis of the polymorphism of the myosin crossbridge and relates it to the Lymn-Taylor crossbridge cycle. Myosin from muscle (myosin II) consists of two long polypeptide chains (heavy chains) combined with four light chains. In cross-striated muscle, the tails of the molecules pack together to form the thick filaments, while the crossbridges that are ATPases point away from the thick filaments and cyclically interact with the actin filaments, moving them along by a kind of rowing action. The fuel for this process is provided by the hydrolysis of adenosine triphosphate (ATP). There are three primary conformations of the myosin crossbridge that can be associated with states in the Lymn-Taylor cycle. These are-namely, the post-rigor structure, the prepower stroke structure, and the rigor-like state. A comparison of these structures leads to the identification of various important conformationally flexible elements, such as (1) the positions of the converter domain, (2) the kink in the relay helix, and (3) the degree of twist of the central β-sheet. The chapter describes these states and then presents the biochemical and kinetic arguments for assigning them to the positions shown in the Lymn-Taylor cycle.