5 Difference between Troponin and Tropomyosin (With Table)

Muscular contraction and relaxation usually enhance movement in animals. The rhythmic movement happens within the muscle fibers. 

These muscle fibers consist of myofibrils that have long proteins arranged in sarcomeres. These are the building blocks of striated muscle tissue. 

Sarcomere composed of thick and thin filaments of actin and myosin proteins. These filaments are arranged next to each other in the sarcomere. 

The interaction of thick and thin filaments happens to be responsible for the contraction and relaxation of muscles. Calcium ions help to spearhead the contraction of muscles. 

So, what is the main difference between troponin and tropomyosin? The former is a complex protein regulatory that comprises troponin T, C, and I whereas the latter is a double-stranded protein coil located within the groove between actin filaments in muscle tissue. 

Research shows that troponin is attached to tropomyosin which controls the contraction of cardiac and skeletal muscles in animals. Calcium ion concentration causes muscle contraction and low amount results in relaxation of muscles. 

This article provides deeper insight into the differences between troponin and tropomyosin in a tabular form. Keep reading to find out the relationship between troponin and tropomyosin in smooth muscle. 

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Comparison Table (Troponin vs Tropomyosin)

Basic Terms Troponin Tropomyosin 
Description It is a globular protein complex that enhances muscle contraction. It is a protein type related to myosin which is involved in muscular contraction. 
Structure Complex with three regulatory proteins:Double-stranded, alpha-helical, and coiled protein located in the groove between the actin filaments of muscle tissue. 
Function Bind two calcium ions to move away tropomyosin from the myosin-binding sites on actin filaments. Covers myosin-binding sites on actin filaments to prevent contraction. 
Calcium Ions Effect High calcium ions concentration enhances muscular contraction Low calcium ion concentrations cause muscular relaxation. 
Types Troponin T

Troponin C

Troponin I 

Muscle tropomyosin isoforms

Non-muscle tropomyosin isoforms. 

What Is Troponin?

It is a complex with three regulatory proteins that facilitate the contraction of cardiac and skeletal muscles in animals. The regulation of muscle contraction happens via calcium binding in the actin filaments. 

A high concentration of calcium ions and ATP causes sarcomere contraction. It happens since calcium ions bind on troponins. 

The binding of calcium ions to troponins triggers the exposure of myosin-binding sites on the actin filaments. It later helped to remove tropomyosin from the actin filaments. 

Myosin has thick filaments that bind with actin that have thin filaments. The thin filaments are pulled towards the center to make the sarcomere short and contract. 

Troponin is responsible for muscular contraction. Troponin occurs as a complex of three regulatory proteins as troponin T, troponin C, and troponin I. 

What Is Tropomyosin?

It is a double-stranded regulatory protein associated with smooth and thin filaments of myofibrils. The protein regulatory occurs in the groove between the actin filaments. 

It is responsible for covering the binding sites of myosin on the actin filaments at rest. The purpose is to enhance muscle relaxation and prevent muscle contraction. 

Action potential usually stimulates the muscle cells to open calcium channels to release calcium in the sarcoplasm via a sarcoplasmic membrane. 

The released calcium ions end up binding with troponins to change the conformation. The calcium-bound troponins later move tropomyosin away from the myosin-binding sites on the actin filaments. 

The binding of actin to myosin filaments results in cross-bridge formation. The event later facilitated the contraction of muscle fibers. 

The Main groups of tropomyosin are muscle tropomyosin and non-muscle tropomyosin isoforms.  Muscle tropomyosin isoform facilitates muscle contraction and non-muscle tropomyosin regulates cytoskeletal and other cellular functions. 

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Main Difference between Troponin and Tropomyosin

  1. Troponin is involved in muscular contraction while tropomyosin is involved in muscular relaxation. 
  2. Troponin exposes myosin-binding sites in the actin filaments whereas tropomyosin covers the active sites on the actin filaments. 
  3. Groups of troponin complex regulatory proteins are troponin T, C,  and I while those of tropomyosin are muscle tropomyosin isoforms and non-muscle tropomyosin isoforms. 
  4. High calcium ions concentration in troponin result in muscular contraction while low calcium ions concentration in tropomyosin causes muscle relaxation. 

Similarities between Troponin and Tropomyosin

  1. Both are complex regulatory proteins. 
  2. Both occur in cardiac and skeletal muscles. 
  3. Both regulate sarcomere contraction via calcium-binding. 
  4. Dysfunction of both results in numerous disease conditions. 

Frequently Asked Questions

Can Troponin be Elevated without a Heart Attack?

Absolutely. The diagnostic marker of the damaged heart usually happens if the patient has not experienced a heart attack. 

Can Troponin be Elevated in Unstable Angina?

Yes. Elevated cardiac troponin levels are common in patients having unstable angina. The patients have a non- neglectable risk of adverse cardiovascular events.

Are Troponin and Tropomyosin Regulatory Proteins?

Absolutely. Troponin is responsible for regulating tropomyosin by activating calcium-binding sites in the actin filaments. 

Are Troponin Tests Expensive?

The average cost per test ranges from $12 to $50. But this usually depends on your geographical location and the medical officer taking the cardiac biomarker testing. 

Why Is Tropomyosin Important?

It helps to regulate muscle contraction and relaxation through the interaction of actin, myosin, and troponin complex. The changes in tropomyosin phosphorylation occur both postpartum and in response to cardiac hypertrophy and heart failure.

What Is the Function of Tropomyosin?

It is responsible for regulating muscular contraction and relaxation in the cardiac and skeletal muscles. It happens due to the interaction of myosin, actin, and troponin complex. 

Are Troponin and Tropomyosin the Same?

Absolutely. Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue. But the functions of these two regulatory proteins are different. 

In Conclusion

Troponin is a complex regulatory protein that consists of troponin T, troponin C, and troponin I. It also gets attached to smooth filaments of tropomyosin to cover the myosin-binding sites on the actin filaments. 

Tropomyosin helps to prevent the contraction of cardiac and skeletal muscles at rest. It happens when the troponin bound with calcium ions removes the tropomyosin away from the actin filaments to expose myosin-binding sites. 

The core difference between troponin and tropomyosin is based on their structure and function. I hope this article was helpful regarding these complex regulatory proteins. 

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