Evidence for the lack of direct phosphorylation of bovine caudate tyrosine hydroxylase following activation by exposure to enzymatic phosphorylating conditions

Highly purified bovine caudate tyrosine hydroxylase can be activated by exposure to enzymatic phosphorylating conditions. This activation is due to both a decrease in the K_m for the pterin cofactor and to some increase in V_max. The K_m for the enzyme's substrate, tyrosine, is unchanged by activation. After tyrosine hydroxylase was activated in the presence of [γ-³²P]-ATP, no incorporation of ³²P into the enzyme was observed by either immunoprecipitation studies or by sucrose gradient studies.