title: Methylamine dehydrogenase is a light-dependent oxidase.
abstract: Quinoproteins may function either as oxidases or dehydrogenases, depending on the nature of their quinone prosthetic group. The tryptophan tryptophylquinone (TTQ)-linked methylamine dehydrogenase (MADH) is relatively inert towards O2 in its reduced form. It is shown that on exposure to long range UV (ultaviolet) light, MADH is oxidized in the presence of O2 and exhibits substrate-dependent steady-state oxidase activity. The effects of light are completely reversible, and oxidase activity is lost when the light is turned off. The light-dependent oxidation of MADH proceeds via a semiquinone intermediate which accumulates to near stoichiometric levels. The absorption of the light appears to provide energy to overcome a thermodynamic barrier to the transfer of an electron from TTQ to O2. These studies provide a basis for understanding what factors dictate whether an oxidoreductase is a dehydrogenase or an oxidase.
authors.affiliation: Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216-4505, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhu
authors.forename: V L
authors.initials: VL
authors.lastname: Davidson
mesh_terms: D008027:Light; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors
chemical_list: C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors