Amino acid-derived hormones, also known as amine hormones, share properties like being mostly hydrophilic and typically acting via second messenger systems. Let's explore their properties in more detail:
Key Properties of Amino Acid Derived Hormones
Amino acid derived hormones are synthesized from the amino acids tyrosine and tryptophan. Due to their structural similarity to amino acids, they exhibit specific characteristics:
-
Hydrophilic Nature: Most amino acid-derived hormones are water-soluble (hydrophilic). This property affects how they travel in the bloodstream and interact with target cells.
-
Transport in Blood: Being hydrophilic, these hormones can readily dissolve in the blood plasma for transport throughout the body. This eliminates the need for carrier proteins (unlike steroid hormones, which are lipophilic).
-
Receptor Location: Since they are not lipid-soluble, amino acid-derived hormones cannot diffuse across the cell membrane to bind to intracellular receptors. Instead, they bind to receptors located on the cell surface.
-
Mechanism of Action: Binding to a cell surface receptor triggers a signaling cascade inside the cell. This often involves second messenger systems, such as cyclic AMP (cAMP), inositol trisphosphate (IP3), or calcium ions (Ca2+). These second messengers amplify the signal and initiate the cellular response.
-
Rapid Action: The effects of amino acid-derived hormones are generally rapid and short-lived due to the signal transduction pathways they activate.
Examples of Amino Acid Derived Hormones and Their Properties
Here’s a table summarizing some examples and their key characteristics:
| Hormone | Derived From | Hydrophilic/Lipophilic | Receptor Location | Mechanism of Action | Examples of Effects |
|---|---|---|---|---|---|
| Epinephrine (Adrenaline) | Tyrosine | Hydrophilic | Cell Surface | cAMP Second Messenger | Increased heart rate, bronchodilation, glycogen breakdown |
| Norepinephrine (Noradrenaline) | Tyrosine | Hydrophilic | Cell Surface | cAMP Second Messenger | Vasoconstriction, increased heart rate, glycogen breakdown |
| Thyroxine (T4) | Tyrosine | Lipophilic (requires transport protein) | Intracellular | Gene transcription | Increased metabolic rate, growth, and development |
| Triiodothyronine (T3) | Tyrosine | Lipophilic (requires transport protein) | Intracellular | Gene transcription | Increased metabolic rate, growth, and development |
| Melatonin | Tryptophan | Relatively Lipophilic | Intracellular and cell surface receptors | Multiple mechanisms involving G proteins | Regulation of sleep-wake cycles, antioxidant properties |
Note: Although most sources consider thyroid hormones (T3 and T4) as derived from amino acids, they behave more like steroid hormones due to their ability to cross cell membranes and interact with intracellular receptors. Melatonin, while derived from tryptophan, has both cell surface and intracellular receptor interactions.
Summary
Amino acid-derived hormones are primarily hydrophilic, allowing them to travel freely in the bloodstream and bind to receptors on the surface of target cells. This interaction initiates a cascade of events mediated by second messengers, resulting in a rapid cellular response. Exceptions like thyroid hormones demonstrate the diverse ways in which these hormones can function.
