Final answer:
Troponin is a protein found in myocardial cells, crucial for muscle contraction by binding to calcium ions and tropomyosin, facilitating the contraction process. It is not an enzyme or amino acid. CPK, involved in energy production for muscle contraction, is also a marker for myocardial infarction.
Step-by-step explanation:
Troponin is a protein found in myocardial cells that plays a critical role in muscle contraction. Specifically, troponin is part of the troponin complex, consisting of three subunits: troponin C, troponin I, and troponin T. Troponin T binds to tropomyosin, another protein associated with actin filaments in muscle fibers, and troponin I acts as an inhibitory subunit. The troponin C subunit binds to calcium ions that are released during muscle excitation, which causes a conformational change in the troponin complex, leading to the movement of tropomyosin and the exposure of myosin binding sites on the actin filament. This process triggers muscle contraction.
Creatine phosphokinase (CPK), also important to muscular function, is an enzyme that catalyzes the production of creatine phosphate, an energy-carrying molecule used during muscle contraction. CPK rises quickly in the blood plasma following a myocardial infarction or heart attack, making it a significant marker for diagnosis. However, troponin is considered more specific for myocardial injury than CPK.