Practice question

Actomyosin ATPase cycle illustrates chemomechanical coupling. Starting rigor actin myosin complex with empty nucleotide pocket tightly bound, ATP binding induces opening of actin binding cleft and dissociation rate 1000 per second. Free myosin closes Switch I Switch II around gamma phosphate hydrolyzing ATP to ADP inorganic phosphate with rate 50 per second, coupled to recovery stroke where lever arm swung 90 degrees from post stroke to pre stroke position, converter domain rotation storing elastic energy, myosin primed high energy configuration. This hydrolysis induced conformational change essential; without hydrolysis myosin would remain unprimed unable to generate force upon rebinding. Myosin ADP Pi then weakly attaches actin, strong binding and phosphate release drive power stroke, ADP release returns rigor. Actin filament does not depolymerize during cycle, actin stable scaffold, ADP release separate step after power stroke. Therefore ATP hydrolysis drives myosin head undergoing conformational change cocking lever arm into energized state preparing for phosphate gated power stroke that performs mechanical work during contraction.