title: Two apparent molecular weight forms of human and monkey phenylalanine hydroxylase are due to phosphorylation.
abstract: Two-dimensional polyacrylamide gel analyses of purified human and monkey liver phenylalanine hydroxylase reveal that the enzyme consists of two different apparent molecular weight forms of polypeptide, designated H (Mr = 50,000) and L (Mr = 49,000), each containing three isoelectric forms. The two apparent molecular weight forms, H and L, represent the phosphorylated and dephosphorylated forms of phenylalanine hydroxylase, respectively. After incubation of purified human and monkey liver enzyme with purified cAMP-dependent protein kinase and [gamma-32P]ATP, only the H forms contained 32P. Treatment with alkaline phosphatase converted the phenylalanine hydroxylase H forms to the L forms. The L forms but not the H forms could be phosphorylated on nitrocellulose paper after electrophoretic transfer from two-dimensional gels. Phosphorylation and dephosphorylation of human liver phenylalanine hydroxylase is not accompanied by significant changes in tetrahydrobiopterin-dependent enzyme activity. Peptide mapping and acid hydrolysis confirm that the apparent molecular weight heterogeneity (and charge shift to a more acidic pI) in human and monkey liver enzyme results from phosphorylation of a single serine residue. However, phosphorylation by the catalytic subunit of cAMP-dependent protein kinase does not account for the multiple charge heterogeneity of human and monkey liver phenylalanine hydroxylase.
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D000882:Haplorhini; D006801:Humans; D007525:Isoelectric Focusing; D008099:Liver / Q000201:enzymology; D008970:Molecular Weight; D010651:Phenylalanine Hydroxylase / Q000032:analysis*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D014357:Trypsin / Q000378:metabolism
chemical_list: D010651:Phenylalanine Hydroxylase; D010744:Phosphoric Monoester Hydrolases; D014357:Trypsin