Isozymes of phenylalanine hydroxylase

Three isozymes of phenylalanine hydroxylase exist in adult rat liver. They are chromatographically unique. Partial chracterization suggests that they are similar in chemical properties and differ only in charge. Estimation of the Stokes radii indicates that the isozymes have similar molecular weights of about 200,000. Two isozymes exist in human fetal liver. Alterations of the relative amounts of these isozymes may control the phenotype of the disease phenylketonuria.