Active site and conformation-directed photoinactivation of copper-dependent oxidoreductases: studies of pig kidney diamine oxidase and Agaricus bisporus tyrosinase.

Abstract

Pig kidney diamine oxidase and Agaricus bisporus tyrosinase were observed to be irreversibly inactivated by 253.7 nm ultraviolet (UV) radiation. By means of hydrodynamic and UV spectral studies, the direct accessibility of the catalytic center of diamine oxidase to UV radiation has been shown to be a possible route for the photoinactivation of this oxidase. Fluorescence and thermal denaturation studies indicated that UV, radiation by perturbing the major molecular forces, destabilizes and unfolds the natural structure of tyrosinase, which in turn leads to the inactivation of this enzyme. A comparative analysis of the inactivation data of the two oxidases revealed that photoinactivation was a very complex, “conformation directed” phenomenon involving the disruption of intramolecular forces and the unfolding of the compact and globular conformation of the natural enzyme.