amine hormone

An amine hormone is built from a single amino acid rather than a chain of them — a small molecule made by chemically remodeling one building block. Most are derived from the amino acid tyrosine. This single class is unusual because its members behave in two opposite ways depending on small structural differences.

The catecholamines — epinephrine, norepinephrine, and dopamine — are water-soluble. Like peptide hormones, they are stored in granules, released quickly, travel freely in blood, and act on cell-surface receptors to produce fast effects, as in the fight-or-flight response. Thyroid hormones, although also made from tyrosine, behave like steroids instead: they are fat-soluble, need carrier proteins to travel, and act on receptors inside the cell.

This split makes amine hormones a useful reminder that the chemical category of a hormone does not always predict its behavior — what matters most for transport and action is whether the finished molecule is water-loving or fat-loving.