Enthalpy of nucleotides binding to myosin

Area of Science:

• Biochemistry
• Molecular Biology
• Muscle Physiology

Background:

• Myosin, a key motor protein, utilizes ATP hydrolysis for muscle contraction.
• Understanding the energetics of nucleotide binding and hydrolysis is crucial for elucidating myosin's function.
• Enthalpy measurements provide direct thermodynamic insights into biochemical processes.

Purpose of the Study:

• To determine the binding enthalpies of adenosine 5 '-diphosphate (ADP) and 5 '-adenylyl imidodiphosphate [AMP-P(NH)P] to rabbit skeletal myosin.
• To characterize the thermodynamic phases of ATP reaction with myosin, including binding, hydrolysis, and product release.

Main Methods:

• Isothermal titration calorimetry was used to measure binding enthalpies.
• Experiments were conducted in Pipes and Tris buffers at pH 7.8 and 15°C.
• Enthalpy changes were resolved into distinct kinetic phases.

Main Results:

• ADP binding to myosin was exothermic.
• AMP-P(NH)P, a non-hydrolyzable ATP analog, exhibited a small, endothermic binding enthalpy.
• ATP reaction with myosin showed a fast, endothermic phase (binding and hydrolysis) and a slow, exothermic phase (product release).

Conclusions:

• The thermodynamic profiles of nucleotide binding and hydrolysis differ significantly.
• The distinct enthalpy phases in ATP turnover highlight the energetics of different steps in the myosin ATPase cycle.
• These findings contribute to understanding the energy transduction mechanisms in muscle contraction.