In Vitro Phosphorylation of Bovine Adrenal Tyrosine Hydroxylase by Adenosine 3’:WMonophosphate-dependent Protein Kinase*

We have studied the effects of adenosine 3’:5’-monophosphate (CAMP)-dependent protein kinase on the phosphorylative and functional modification of bovine adrenal tyrosine hydroxylase. Incubation of partially purified tyrosine hydroxylase with CAMP-dependent protein kinase in the presence of [y-32P]ATP and 5 pM CAMP led to a 3to B-fold activation of tyrosine hydroxylase and to incorporation of [32P]phosphate into protein. When tyrosine hydroxylase preparations activated by exposure to enzymatic phosphorylating conditions were analyzed by sucrose density gradient centrifugation, polyacrylamide gel electrophoresis, and gel electrofocusing, the radioactivity of 32P was coincident with the activity of tyrosine hydroxylase, suggesting incorporation of 32P from [Y-~~P]ATP into tyrosine hydroxylase. Polyacrylamide gel electrophoresis of the phosphorylated tyrosine hydroxylase preparation in the presence of 0.1% sodium dodecyl sulfate revealed that the 60,000-dalton polypeptide subunit of tyrosine hydroxylase served as the phosphate acceptor.