The monoamines are slower-acting and more localized in distribution than the amino acids, and are known to be released from non-synaptic sites. Monoamines are synthesized from a single amino acid (hence mono-amine). There are two broad groups of monoamines: catecholamines and indolamines. Among the catecholamines are dopamine, epinephrine, and norepinephrine, all synthesized from tyrosine, which is then converted to L-dopa and dopamine. Among the indolamines are serotonin (5-hydroxytryptamine, or 5-HT) and melatonin.