Difference Between Tyrosine and Thyroxine

The main difference between tyrosine and thyroxine is that the tyrosine is the precursor amino acid of thyroid hormones while the thyroxine or T4 is the prohormone of the active thyroid hormone. The formation of thyroid hormones occurs in the thyroid gland.  

Tyrosine and thyroxine are two types of precursors of the active thyroid hormone, which regulates the metabolism of the body. Active thyroid hormone is called triiodothyronine or T3. 

Key Areas Covered 

1. What is Tyrosine
     – Definition, Facts, Importance
2. What is Thyroxine
     – Definition, Facts, Importance
3. What are the Similarities Between Tyrosine and Thyroxine
     – Outline of Common Features
4. What is the Difference Between Tyrosine and Thyroxine
     – Comparison of Key Differences

Key Terms 

Regulation of Metabolism, Thyroid Hormones, Thyroxine, Triiodothyronine, Tyrosine 

What is Tyrosine 

Tyrosine is a non-essential amino acid required by the body for the production of thyroid hormones. Though tyrosine is produced by the body from another amino acid called phenylalanine, it is a must to take tyrosine through the diet. Tyrosine is rich in chicken, turkey, fish, dairy products such as cheese.

Figure 1: Tyrosine Metabolism

Apart from thyroid hormones, thyroxine is involved in the production of important substances in the body such as; 

• Dopamine: Neurotransmitter in the brain, important for memory and motor skills 
• Adrenaline/Noradrenaline: Hormones responsible for the fight-or-flight response to stressful situations  
• Melanin: The pigment responsible for the color of the skin, hair, and eyes 

What is Thyroxine 

Thyroxine or T4 is the prohormone of triiodothyronine or T3, which is the active form of thyroid hormone. The active form of the thyroid hormone has a high potency than thyroxine to enter into the cells. Both thyroxine and triiodothyronine are produced by the thyroid gland. Generally, 80% of thyroid hormones produced are T4 while the remaining 20% is T3. A pituitary hormone called TSH stimulates the production of thyroid hormones in the thyroid gland.  

Figure 2: Thyroid Hormone System

The conversion on thyroxine into T3 mainly occurs in the liver by the action of an enzyme called iodothyronine deiodinase. However, each and every cell in the body also contains this enzyme, which converts thyroxine into its active form.

Effects of the Thyroid Hormones on the Body  

• Increases heart rate, ventilation rate, cardiac output, and basal metabolic rate 
• Increases the effects of catecholamines (i.e. increases sympathetic activity) 
• Enhances brain development 
• Thickens endometrium in females 
• Enhances catabolism of carbohydrates and proteins 

Both the excess and the insufficient amounts of thyroid hormones in the body lead to diseases conditions. Hyperthyroidism refers to the collection of symptoms arisen from excess thyroid hormones in the circulation while hypothyroidism refers to the collection of symptoms arisen from the insufficient amounts of thyroid hormones in the circulation.  

Similarities Between Tyrosine and Thyroxine 

• Tyrosine and thyroxine are two types of precursors of the thyroid hormones. 
• Reduced amounts of both of these precursors can affect the triiodothyronine level. 
• Both can be taken into the body as supplements. 

Difference Between Tyrosine and Thyroxine 

Definition 

The tyrosine refers to a hydrophilic amino acid which is a constituent of most proteins and is important in the synthesis of some hormones while the thyroxine refers to the main hormone produced by the thyroid gland, acting to increase metabolic rate and regulating growth and development.  

Type of Molecule 

Tyrosine is an amino acid while thyroxine is a polypeptide. 

Role 

Tyrosine serves as the precursor amino acid for the production of thyroid hormones while thyroxine is the prohormone of the active thyroid hormone, triiodothyronine. 

Synthetic Forms

The synthetic from of tyrosine is L-tyrosine while the synthetic form of thyroxine is the L-thyroxine.

Conclusion 

Tyrosine is a non-essential amino acid, which is one of the precursors of thyroid hormones. On the other hand, thyroxine is the prohormone of the active form of the thyroid hormone. Therefore, the main difference between tyrosine and thyroxine is the type of molecule and their function.

Reference:

1. “Tyrosine: Benefits, Side Effects and Dosage.” Healthline, Healthline Media, Available Here   
2. “Thyroxine.” You and Your Hormones, Available Here

Image Courtesy:

1. “Conversion of phenylalanine and tyrosine to its biologically important derivatives” By LHcheM – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2. “Thyroid system” By Mikael Häggström – All used images are in public domain. (Public Domain) via Commons Wikimedia