Enzymatic Determination of L-Phenylalanine and L-Tyrosine

An enzymatic method for the determination of phenylalanine and tyrosine has been described. This method is based on the formation of cinnamic acid from phenylalanine or the formation of p-coumaric acid from tyrosine by phenylalanine ammonia-lyase of Rhodotorula. Cinnamic acid and p-coumaric acid, which are formed in stoichiometric amounts, are determined spectrophotometrically. Other amino acids and d-isomers of phenylalanine and tyrosine have no effect on this determination.