Loose coupling between chemical and mechanical reactions in actomyosin energy transduction.
In order to study the mechanochemical coupling in actomyosin energy transduction, the sliding distance of an actin filament induced by a myosin head during one ATP hydrolysis cycle was obtained using an in vitro movement assay, which permitted quantitative and simultaneous measurements of (1) the movements of single fluorescently-labeled actin filaments on myosin bound to coverslip surfaces and (2) the ATPase rates. The sliding distance was determined as (the working-stroke time in one ATPase cycle, Tws) x (the filament velocity, v). The working-stroke time (Tws) was obtained from the ATPase turnover rate of myosin during the sliding (kT), the ATP hydrolysis time on myosin heads (delta T) and the ON-rate at which myosin heads enter into the working-stroke when they encounter actin (kON); Tws approximately 1/kT-delta T-1/kON. kON was estimated by analyzing the movements of very short (40 nm) filaments. The resulting sliding distance during one ATP hydrolysis cycle near zero load was greater than 100 nm, which is about 10 times longer than that expected for a single attachment-detachment cycle between an actin monomer and a myosin head. This leads to the conclusion that the coupling between the chemical and mechanical reactions is not rigid in a one to one fashion.
Yanagida
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Department of Biophysical Engineering, Osaka University, Japan.
D000199:Actins / Q000502:physiology / Q000648:ultrastructure; D000205:Actomyosin / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D008854:Microscopy, Electron; D008954:Models, Biological; D009119:Muscle Contraction; D009218:Myosins / Q000502:physiology / Q000648:ultrastructure
D000199:Actins; D000205:Actomyosin; D009218:Myosins