Dopamine, norepinephrine, and serotonin belong to the biogenic amines, and also they are neurotransmitters. Dopamine and norepinephrine are different from serotonin since they are catecholamines, which means that their precursor is tyrosine. All three mentioned neurotransmitters are synthesized through enzyme conversion. So, in the next paragraphs, the process of an enzyme conversion for dopamine, norepinephrine, and serotonin is briefly explored.
As such, for dopamine, the first step of conversion involves a reaction with tyrosine hydroxylase, which is a catalyzer (Purves et al., 2018). DOPA, created after this step, interacts with DOPA decarboxylase (or aromatic L-amino acid decarboxylase). The result of this reaction is dopamine, as shown in Figure 1. Therefore, dopamine is a biogenic amine neurotransmitter synthesized through the two-step conversion of tyrosine.
Next, dopamine substances might be converted into norepinephrine via an enzyme. Precisely, dopamine β-hydroxylase is necessary for the next step of catalysis (Purves et al., 2018). The synthesis is shown in Figure 2, where norepinephrine is formed from dopamine. Hence, norepinephrine is a catecholamine, meaning that it is synthesized in the process of enzyme conversion with tyrosine being a precursor that needs three steps of interaction for a successful reaction.
Finally, serotonin synthesis is different from that of dopamine and norepinephrine. Its precursor is the amino acid tryptophan, which is at first hydroxylated and then catalyzed by tryptophan hydroxylase. Figure 3 depicts the synthesis of serotonin in two steps that have been mentioned. In this way, serotonin is a biogenic amine neurotransmitter, which precursor is tryptophan that undergoes two-step catalysis.