Conversion of Phenylalanine into Tyrosine by Portulaca Callus

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Abstract
The incorporation of [14C]phenylalanine and [1,6-14C]shikimic acid into tyrosine was investigated in the callus of Portulaca grandiflora, var. JR (L.). By inhibiting phenylalanine with 1-α-aminooxy-β-phenyl-propionic acid and tyrosinase with 1-cysteine-HCl and hydrazine-hydrate, the possible synthesis of tyrosine from phenylalanine was demonstrated. Tetrahydropterine sulfate was an effective activator of this pathway and tyrosine accumulation via 4-hydroxy-prephenic acid is regulated by feedback inhibition. l-α-Amminooxy-β-phenylpropionic acid inhibits both phenylalanine ammonia-lyase and the production of phenylalanine from prephenic acid.