Measurement of ATP Turnover during Shortening and Lengthening of Rabbit Psoas Myofibrils Using a Fluorescent ATP analog
In order to study ATP turnover during shortening and lengthening of rabbit psoas myofibrils, we have used fluorescence microscopy in which the displacement of a fluorescent nucleotide analog, 2’(3’)-0-[N-[2-[[Cy3] amido] ethyl] carbamoyl]-adenosine 5′ triphosphate (Cy3-EDA-ATP) bound to cross-bridge on flash photolysis of caged ATP was measured [Chaen et al. (1997) Biophys. J. 73, 2033–2042]1. In the previous paper1, we reported that when a myofibril was imposed to shorten with a constant velocity by a piezoelectric actuator, the nucleotide displacement rate constant initially increased to 0.7 s-1 with increasing shortening velocity and then declined with a further increase in shortening velocity. The rate constant during lengthening measured in the present experiment was found to be not significantly affected. These results suggest that the cross-bridge kinetics show a asymmetrical depenence on the mechanical strain in the cross-bridges, namely, the rate constants are not significantly affected at higher strain during lengthening but depend on the lower strain during shortening.
KeywordsActin Filament Thin Filament Isometric Force Sarcomere Length Myosin Head
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