The regulatory system of the actin-myosin interaction.

According to recent views the active troponin (Tn) complex consists of three components distinguishable by their ability to bind Ca2+ (TnC), to combine with troponyosin (TnT), and to inhibit actomyosin ATPase with ot without Ca2+ (TnI). Addition of Tn to an actin-myosin-tropomyosin system produceas a Ca2+ requirement for ATPase activity. Recent developments bearing on the mechanism both in vitro and in vivo are reviewed in order to correlate biochemical, physiochemical, electron microscopic, and physiological findings. The use of various combination of isolated components considerably helps in pinpointing changes that occur within components (conformational changes) and in the relative positions of interacting moieties. Available data on differences between the skeletal and cardiac system are also discussed.