HYDROLYSIS OF NUCLEOSIDE TRIPHOSPHATES BY MYOSIN DURING TRANSIENT STATE

The production of hydrogen ions during the hydrolysis of nucleotide triphosphates by myosin was determined in a stopped-flow spectrophotometer by measuring the optical density change of an indicator dye. At pH 8, in 0.5 m KC1 with MgATP, MgITP, or CaATP as substrates, hydrogen ions were liberated during the transient phase at rates which greatly exceeded the steady-state rates of hydrolysis. The time course for MgATP at 0° or MgITP at 20° could be fitted by a single rate constant, while two rate constants were required for MgATP at 20° and CaATP at 0°. In the case of MgATP at 20°, both rate constants were proportional to substrate concentration over a range of low substrate concentrations. As substrate concentration was increased above 10-4 m the rates approached limiting values corresponding to rate constants of approximately 130 and 20 sec-1. © 1969, American Chemical Society. All rights reserved.