REGULATION AND CRYSTALLIZATION OF PHOSPHORYLATED AND DEPHOSPHORYLATEDFORMS OF TRUNCATED DIMERIC PHENYLALANINE-HYDROXYLASE

Phenylalanine hydroxylase is regulated in a complex manner, including activation by phosphorylation. It is normally found as an equilibrium of dimeric and tetrameric species, with the tetramer thought to be the active form. We converted the protein to the dimeric form by deleting the C-terminal 24 residues and show that the truncated protein remain s active and regulated by phosphorylation. This indicates that changes in the tetrameric quaternary structure of phenylalanine hydroxylase a re not required for enzyme activation. Truncation also facilitates cry stallization of both phosphorylated and dephosphorylated forms of the enzyme.