| Abstract: | The kinetics of binding and hydrolysis of ATP by bovine cardiac myosin subfragment 1 has been reinvestigated. More than 90% of the total fluorescence amplitude associated with ATP hydrolysis occurs with an apparent second-order rate constant of 8.1 X 10(5) M-1 S-1 and a limiting rate constant of approximately 140 S-1 (100 mM KCl, 50 mM 1,3-bis-[tris(hydroxymethyl)methylamino]-propane, 10 mM MgCl2, pH 7.0, 20 degrees C); the remaining 10% occurs more slowly (approximately 1 S-1). The observed rate constants are independent of subfragment 1 concentration under pseudo first-order conditions for ATP with respect to protein. The fraction of protein which hydrolyzes ATP rapidly is not a function of the nucleotide or protein concentration and appears to be constant irrespective of ionic strength or temperature within the range studied (50-100 mM KCl, pH 7.0, 15-20 degrees C). These data are compared to that obtained previously using subfragment 1 prepared by a different method which showed ATP-dependent aggregation of two protein species. |
