On the conformational state of photoinactivated tyrosinase: Possibility of structural segments in the enzyme molecule.

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Abstract
Ultraviolet irradiation of tyrosinase rapidly decreased the dopa oxidase activity of the enzyme. Hydro-dynamic, kinetic and thermodynamic parameters revealed gross differences in the native and photoinactivated states of the enzyme. The native state of tyrosinase was characterized as a tetramer with a compact, globular and rigid conformation. However, the photoinactivated state of tyrosinase was thermodynamically less stable and unusually sensitive to temperatures as low as 35°C. From the dose dependent loss in conformational integrity, thermodynamic stability and catalytic activity of tyrosinase, it is speculated that there are various structural segments distributed throughout the enzyme molecule. These structural segments act as centres of major molecular forces which hold the tetrameric enzyme into a compact and globular conformation. UV modification of these segments triggers a series of conformational changes leading to formation of a partially unfolded and catalytically inactive form of tyrosinase.

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