McNamara James W, Li Amy, Dos Remedios Cristobal G, Cooke Roger
Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Sydney, 2006, Australia.
Department of Biochemistry & Biophysics, Cardiovascular Research Institute University of California, San Francisco, CA, 94158-2517, USA.
Biophys Rev. 2015 Mar;7(1):5-14. doi: 10.1007/s12551-014-0151-5. Epub 2014 Dec 20.
The super-relaxed (SRX) state of myosin was only recently reported in striated muscle. It is characterised by a sub-population of myosin heads with a highly inhibited rate of ATP turnover. Myosin heads in the SRX state are bound to each other along the thick filament core producing a highly ordered arrangement. Upon activation, these heads project into the interfilament space where they can bind to the actin filaments. Thus far, the population and lifetimes of myosin heads in the SRX state have been characterised in rabbit cardiac, and fast and slow skeletal muscle, as well as in the skeletal muscle of the tarantula. These studies suggest that the role of SRX in cardiac and skeletal muscle regulation is tailored to their specific functions. In skeletal muscle, the SRX modulates the resting metabolic rate. Cardiac SRX represents a "reserve" of inactive myosin heads that may protect the heart during times of stress, e.g. hypoxia and ischaemia. These heads may also be called up when there is a sustained demand for increased power. The SRX in cardiac muscle provides a potential target for novel therapies.
肌球蛋白的超松弛（SRX）状态直到最近才在横纹肌中被报道。它的特征是肌球蛋白头部的一个亚群具有高度受抑制的ATP周转速率。处于SRX状态的肌球蛋白头部沿着粗肌丝核心相互结合，形成高度有序的排列。激活后，这些头部伸入肌丝间空间，在那里它们可以与肌动蛋白丝结合。到目前为止，已在兔心脏、快肌和慢肌骨骼肌以及狼蛛的骨骼肌中对处于SRX状态的肌球蛋白头部的数量和寿命进行了表征。这些研究表明，SRX在心脏和骨骼肌调节中的作用是根据它们的特定功能量身定制的。在骨骼肌中，SRX调节静息代谢率。心脏SRX代表无活性肌球蛋白头部的一种“储备”，在应激状态下，如缺氧和缺血时，可能保护心脏。当对增加功率有持续需求时，这些头部也可能被调用。心肌中的SRX为新型疗法提供了一个潜在靶点。
