Amino acids and their metabolites participate in signal transduction process - hormonal control and the synaptic transmission of nerve impulses. Some compounds, like epinephrine and histamine (see here) participate in both processes.

Glycine and glutamate are amino acids that serve directly as neurotransmitters are. -Aminobutyric acid (GABA), the decarboxylation product of glutamate, is also a neurotransmitter. Amino acid metabolites that function in neurotransmission include histamine (from histidine), serotonin (from tryptophan), and catecholamines (epinephrine, dopamine, and norepinephrine), which are derived from tyrosine.

Serotonin - The metabolic biosynthetic pathway from tryptophan to serotonin is shown here. Serotonin plays multiple roles in the nervous system, including neurotransmission. It is a precursor to melatonin, which is involved in the regulation of sleepiness and wakefulness. In the intestine, serotonin regulates intestinal peristalsis. Serotonin is also a potent vasoconstrictor, which helps regulate blood pressure.

Catecholamines - Figure 21.32 depicts the pathway to catecholamines from tyrosine.

1. Neurotransmitter Receptors and Their Effects

2. Neurotransmitter Newsletter