Phenylalanine

Phenylalanine is an essential aromatic amino acid and the metabolic precursor to tyrosine and the catecholamine neurotransmitters, with circulating levels rising when net muscle protein breakdown exceeds synthesis. In saliva, phenylalanine serves as an index of proteolytic balance and amino-acid release following muscular work. Yi et al. (2025) identified salivary phenylalanine among the metabolites that vary after high-intensity rowing and screen for exercise-induced muscle damage.