The tetrahydrobiopterin-dependent iron-enzyme tyrosine hydroxylase (TH) catalyses the rate-limiting step in catecholamine biosynthesis. Electron paramagnetic resonance (EPR) data show that following phosphorylation of Ser-40 by protein kinase A, the enzyme-bound Fe(III), coordinated to catecholamines, can be reduced by 6-methyl-tetrahydropterin under turnover conditions. The 8-fold increase in product formation upon phosphorylation can partly be explained by an increase in the fraction of active TH, by dissociation of the endogenous catecholamine inhibitors. © 1989.
Andersson, K. K., Haavik, J., Martinez, A., Flatmark, T., & Petersson, L. (1989). Evidence from EPR spectroscopy that phosphorylation of Ser-40 in bovine adrenal tyrosine hydroxylase facilitates the reduction of high-spin Fe(III) under turnover conditions. FEBS Letters, 258(1), 9–12. https://doi.org/10.1016/0014-5793(89)81603-5