What binds to Troponin in skeletal muscles to facilitate myosin's readiness for ATP binding?

In skeletal muscles, calcium ions (Ca2+) play a crucial role in the contraction process by binding to troponin, which is a regulatory protein associated with actin filaments. When muscle fibers are stimulated to contract, calcium is released from the sarcoplasmic reticulum into the cytosol of the muscle cell. This increase in calcium concentration allows Ca2+ to bind to troponin.

The binding of calcium to troponin causes a conformational change in the troponin-tropomyosin complex, which ultimately exposes the myosin-binding sites on the actin filaments. This exposure is vital for muscle contraction, as it enables myosin heads to attach to actin. Once the myosin heads bind to actin, they go through a series of movements that utilize ATP, leading to muscle contraction.

This mechanism is fundamental to the sliding filament theory of muscle contraction, where the interaction between actin and myosin is key to muscle functionality. Therefore, Ca2+ is essential for triggering the events that lead to myosin's readiness for ATP binding and, consequently, muscle contraction.