Modification of the multiple forms of rat hepatic phenylalanine hydroxylase by in vitro phosphorylation

The two major forms of rat liver phenylalanine hydroxylase have been isolated and partially purified. The tetrahydrobiopterin-dependent activity of these forms can be differentially stimulated by exposure to enzymatic phosphorylating conditions. This in vitro treatment is associated with incorporation of 32p into the enzymes and generates a further, chromatographically distinct, species. These results suggest that the multiple forms of rat liver phenylalanine hydroxylase are due to different degrees of phosphorylation.