Final answer:
Myosin subfragment 1 (S1), or the myosin head, serves as an ATPase enzyme that interacts with actin filaments to facilitate muscle contraction. It uses ATP hydrolysis to induce a power stroke that shortens the muscle. The S1 fragments also help to identify actin in different cell types by the 'decoration' method.
Step-by-step explanation:
Myosin subfragment 1 (S1)
, commonly referred to as the
myosin head
, is a component of myosin that functions as an ATPase, which interacts with actin filaments during muscle contraction. Proteolytic enzymes can separate myosin into S1 and tail fragments. The S1 fragments exhibit ATPase activity specifically when they interact with actin, wherein they hydrolyze ATP to ADP, allowing the
power stroke
during muscle contraction. Myosin heads undergo an allosteric change utilizing the energy from ATP hydrolysis. This change enables the myosin heads to pull the actin filaments toward the center of the sarcomere, known as the M line, causing the muscle to contract. Additionally, S1 myosin heads can decorate actin filaments in various cell types, revealing that the decorated filaments are a form of F-actin involved in cell motility.
During the contraction cycle, the ATP-myosin binding releases the energy stored in the high-energy myosin conformation. This energy release facilitates the power stroke, whereby the myosin head moves, pulling the actin filament along with it. The resulting movement of the filaments is essential for muscle contraction. After the power stroke, ATP binds to myosin, allowing the muscle to relax and stretch, preparing the myosin heads for the next round of contraction.