Now L-Tyrosine with L-Tyrosine is an essential amino acid formed from Phenylalanine through an enzyme called phenylalanine hydroxylase. This amino acid acts as a precursor to catecholamines (Epinephrine, Norepinephrine and Dopamine), thus justifying its importance in the regulation of the Nervous System. Catecholamines are neurotransmitters involved in the ability to alert and focus, relaxation and mood.