A transient kinetic study of enthalpy changes during the reaction of myosin subfragment 1 with ATP.

Abstract

1. The enthalpy changes during individual reaction steps of the myosin subfragment 1 ATPase were studied with the use of a new stopped-flow calorimeter [Howarth, Millar & Gutfreund (1987) Biochem. J. 248, 677-682]. 2. At 5 degrees C and pH 7.0, the endothermic on-enzyme ATP-cleavage step was observed directly (delta H = +64 kJ.mol-1). 3. ADP binding is accompanied by a biphasic enthalpy change. 4. The release and uptake of protons was investigated by the use of two buffers with widely different heats of ionization. 5. Protons are involved in all four principal steps of the myosin subfragment 1 ATPase.

Calorimetric Determination of Thermodynamic Parameters of Reaction Reveals Different Enthalpic Compensations of the Yeast Hexokinase Isozymes

“…Isothermal titration calorimetry is a very sensitive technique for the direct determination of thermodynamic and kinetic parameters of enzymatic reactions, based on the measurement of the heat, absorbed or release, in a chemical reaction of binding, dilution, or transformation. ITC has been used for the determination of thermodynamic (41,42,(45)(46)(47) as well as kinetic (41, 48 -52) parameters of different enzymes.…”

Structural Mechanism of Muscle Contraction

“…The small free-energy change for step 3 is known to be composed of large compensatory changes in enthalpy and entropy so that although there is only a small net change in ∆G, energy is being converted/stored in this step (69,70).…”

Ergodic pumping: A mechanism to drive biomolecular conformation changes

“…Contrary to the cartoon of [62], hydrolysis of ATP in the ATP-binding pocket of myosin does not liberate a flash of energy which is then stored in some unidentified place such as vibrations or springs and released later as work in the power stroke. In fact, the hydrolysis of ATP in the myosin pocket is endothermic ( H = +27kT ) and reversible with an equilibrium constant of about 10 [2,43] (so G = −2.3kT ). Thus, an amount T S = +29kT of heat is sucked in from the environment on hydrolysis.…”

“…The P carries a charge of between -1 and -2. The believed in-line hydrolysis reaction produces HPO 2− 4 + H + [30], but pK a for the H 2 PO − 4 to HPO 2− 4 transition is about 6.8 and the hydrolysis is observed to release 0.4 H + [43], so perhaps 60% of the 2− form is converted to 1−. Outside the myosin, the pH is about 7.2, so we would expect 75% of the P to end up as 2− (though [47] suggest P is released as 1−).…”

“…10 MPa external pressure reduces tension by 10% [15]. pH also has effects [43,3] (the power stroke releases about 0.4 of a proton). There are effects of chemical modification of SH1 and SH2 [55,42] and effects of replacing Mg 2+ by Ca 2+ or K + [56].…”