CrossBridgeZyklus

CrossBridgeZyklus is a concept in molecular biophysics describing the cyclic interaction between actin filaments and myosin heads that drives force generation in muscle fibers and in many non-muscle cells. The term is often used in German-language literature and is broadly equivalent to the classical cross-bridge cycle, in which ATP hydrolysis provides the energy stored in the myosin head through a conformational change.

The cycle begins when a myosin head detaches from actin in the presence of bound ATP. ATP is hydrolyzed to adenosine diphosphate and inorganic phosphate, which primes the head into a high-energy, “cocked” conformation. Reassociation with a nearby actin binding site leads to a strong interaction, followed by the release of phosphate and the execution of a power stroke that pulls the actin filament relative to the myosin. Release of ADP completes the cycle and returns the head to a rigor-like state, ready to bind ATP again and restart detachment.

The rate and outcome of the CrossBridgeZyklus are regulated by calcium concentration and regulatory proteins such as troponin and tropomyosin (in striated muscle), as well as by the load on the filament, temperature, and the specific myosin isoform involved. Different muscle fiber types exhibit distinct duty cycles and kinetic rates, enabling a range of contraction velocities and force profiles.

In research and applications, the CrossBridgeZyklus serves as a foundational framework for understanding muscle physiology, intracellular transport by myosin motors, and the design of biomimetic molecular machines. It is studied using kinetic modeling, single-molecule assays, and structural methods.