Oxygen free-radicals mediate the damaging effect of ultraviolet light on membrane mitochondria.

This paper reports evidence that exposure of mitochondria to near-ultraviolet light inhibits electron transport, collapses the electric gradient, and increases non-specific membrane permeability to matrix solutes such as Ca2+. Membrane energization, as well as superoxide dismutase and catalase avoid membrane leakiness. Increased permeability correlates with a diminution in the titrated thiol groups. Plausibly the pore is formed through the formation of sulfhydryl bridges by the action of UV light-derived oxygen-centered free- radicals on membrane proteins.