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Tropomyosin and troponin are regulatory proteins in muscle contraction. Tropomyosin action occurs when muscles are resting. Troponin action occurs via calcium binding in the presence of a nervous input.

Enzyme action occurs and gives off a product as substrate binds to enzyme forming the enzyme-substrate complex. Such an enzyme action can be inhibited using inhibitors such as competitive and non-competitive inhibitors. The inhibitors either block the enzyme's active site or alter the enzyme's shape to inhibit the enzyme action.

In competitive inhibition, a competitive inhibitor imitates the substrate and competes for the active site forming an enzyme-inhibitor complex and thus inhibiting the enzyme action owing to the accumulation of products. The substrate cannot bind to the enzyme as the active site gets occupied by the competitive inhibitor.

Tropomyosin covers the myosin-binding sites on actin molecules during the resting state. It prevents cross-bridge formation, and hence no contraction occurs. In the presence of a nervous input, muscle contraction gets enabled by troponin that regulates tropomyosin.

The troponin binds to the tropomyosin and changes the latter's structure.Hence, troponin frees the myosin-binding site on the actin molecule. As a result, cross-bridging occurs between actin and myosin, allowing muscle contraction.

As long as calcium ions and ATP are present, contraction occurs. Depletion of these molecules causes tropomyosin to mask the binding sites on actin again and stop the contraction.

In this way, a comparison between the action of regulatory proteins in muscle contraction and the activity of a competitive inhibitor and substrate in enzyme action is possible as they are involved in regulatory action.