MUSCLE PHYSIOLOGY

Detailed explanation-1: -The addition of regulatory proteins, troponin and tropomyosin, is known to increase the sliding speed of thin filaments in the in vitro motility assay.

Detailed explanation-2: -Troponin and tropomyosin are regulatory proteins that help to regulate the interaction between actin and myosin filaments. The binding of the myosin heads to the muscle actin is a highly regulated process. When a muscle is resting, actin and myosin are separated.

Detailed explanation-3: -The regulatory proteins tropomyosin and troponin are bound to actin in the molar ratio 1:1:7. Tropomyosin is almost entirely -helical coiled coil, and binds in the groove between the two actin strands of the thin filament, so that there are two tropomyosin molecules in every 38-nm repeat of the filament.

Detailed explanation-4: -Troponin plays a central role in the calcium-regulation of muscle contraction: Troponin is the sole calcium-binding component of thin filaments (actin-tropomyosin-troponin complex) of striated muscles.

Detailed explanation-5: -The muscle tropomyosin works in low calcium levels. When the concentration of calcium is low in cells, the tropomyosin proteins remain bound to the troponin proteins. This binding covers the site of actin and myosin interaction, and hence muscle contraction does not occur.