[Detection of phenylalanine hydroxylase activity in leukocytes and fibroblasts]

Phenylalanine hydroxylase activity measured in leucocytes and fibroblasts by the fluorometric method is nonspecific and can be released by other aromatic hydroxylases. Investigations with the inhibitors p-Cl-phenylalanine, 3-I-tyrosine and 6-F-tryptophan made evident that these results may be caused by the tryptophan hydroxylase and the tyrosine hydroxylase. Phenylalanine hydroxylase activities in leucocytes could also not be measured by radiochemical investigations with [3-14C] phenylalanine (scanner and liquid scintillation technique).