Doctor's Best D-Phenylalanine 500mg 60 CapsulesWhat is D-Phenylalanine?Doctor’s Best D-phenylalanine is a non-protein amino acid related to the essential amino acid L-phenylalanine.D- and L-phenylalanine are structural mirror images of each other.D-phenylalanine is reported to inhibit an enzyme (enk..