Phosphorylation-dephosphorylation of renal phenylalanine hydroxylase.

Phenylalanine hydroxylase (Ec 1.14.16.1) catalyses the initial step of phenylalanine degradation in man and other mammals. Although the liver is the primary location of the enzyme, an appreciable amount is also found in the renal cortex [I]. The regulatory properties of the hepatic enzyme are well known. In the short-term, enzymic activity is controlled by reversible phosphorylation [2]. Glucagon and aadrenergic agents stimulate the phosphorylation of the hepatic enzyme through the action of the cyclic AMPde endent protein kinase [3] and a Ca calmodulin-dependent protein kinase respectively [4]. Little is known about the mechanisms underlying the control of the renal enzyme. In particular, the role of reversible phosphorylation, as a regulatory process of physiological significance, remains to be established