Solubilization and Partial Purification of Tyrosine Hydroxylase from Bovine Adrenal Medulla

TLDR

Abstract

Abstract Tyrosine hydroxylase from bovine adrenal medulla has been solubilized and extensively purified. The catalytic properties of the solubilized, purified enzyme are similar to those of the particulate enzyme. The stoichiometry of the reaction catalyzed by the enzyme, as well as its regulatory properties, have been found to vary with different pterin cofactors. The enzyme, for example, is markedly inhibited by its substrate, tyrosine, in the presence of tetrahydrobiopterin, but not in the presence of 6,7-dimethyltetrahydropterin. Purified tyrosine hydroxylase is sensitive to H2O2 that is generated during the nonenzymatic oxidation of tetrahydropterin. The enzyme can be protected by catalase, peroxidase, or Fe2+ from H2O2-mediated inactivation. In the presence of catalase or peroxidase, Fe2+ does not stimulate the reaction. It is concluded that the previous reports that tyrosine hydroxylase is stimulated by Fe2+ can be explained by the known ability of Fe2+ to decompose H2O2