The immunological evidence for a phenylalanine hydroxylase like immunoreactive protein in different human cells and...

Phenylalanine hydroxylase (PAH) was purified 105-fold from human liver. The rel mol mass of the subunits in sodium dodecylsulfate-polyacrylamide gel electrophoresis was 54,000 Da and the isoelectric point was estimated to be between pH 5.0 and 5.2. The activity of purified PAH was inhibited by p-Cl-phenylalanine (p-Cl-Phe), 3-J-tyrosine (3-J-Tyr) and 6-F-tryptophane (6-F-Trp) by 73%, 26% and 10%, respectively. The Km value was 0.36 x 10(-3) mol/l for L-Phe and 5.88 x 10(-5) mol/l for the synthetic cofactor dimethyltetrahydrobiopterin (DMPH4). Polyclonal antibodies raised in rabbits against the active human enzyme showed only a slight cross-reaction with purified rat liver PAH. Using the rabbit antibodies an immunoreactive protein with the same mol mass and isoelectric point as purified human liver PAH and PAH from crude liver extract was detected in extracts from kidney, heart, spleen, brain, pancreas, lung, placenta, leucocytes, cultured skin fibroblasts and chorionic villus cells.