The control of aromatic amino acid catabolism and its relationship to neurotransmitter amine synthesis.

The aromatic amino acids are, inter alia, substrates for the synthesis of important neurotransmitters. Although the factors controlling the synthesis of these transmitters are not fully understood, there is evidence that the concentrations, both relative and absolute, of the precursor amino acids in the blood are of some significance. The article reviews the biochemical pathways involved in tryptophan, phenylalanine, and tyrosine metabolism in liver, brain, and other tissues and discusses (1) the major regulatory events in the maintenance of blood concentrations and (2) the effects of diet, load dosing, hormones, and other circulating substances on the fate of the amino acids and on events in the central nervous system.