Cover picture: Muscle contraction is powered by the hydrolysis of ATP by the molecular motor, myosin. However, in relaxed muscle, myosin continues to slowly hydrolyze ATP, analogous to the engine of an idling automobile. By super-resolution microscopy, hydrolysis of single fluorescent ATP molecules was imaged in relaxed skeletal muscle, with two kinetically distinct myosin hydrolysis rates detected. The slower, “super-relaxed” rate was associated with myosin that colocalized with myosin-binding protein C (MyBP-C), a known modulator of muscle contractile function. These findings implicate MyBP-C in the sequestration of myosin motors into the super-relaxed state and, consequently, regulation of resting muscle metabolism and force generation upon activation.

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