In this theoretical-experimental approach, we show using ab initio calculations behavior consistent with the activation of 7-dehydrocholesterol, provitamin D-3, as an initial reactant toward ultraviolet-activated reactions of vitamin D-3. We find using molecular orbital theory that a conformation between the provitamin and the vitamin shows higher conductance than those of the reactant and product. We also find experimental evidence of this electrical character by directly measuring current-voltage characteristics on irradiated and nonirradiated samples of the provitamin. The activation of the provitamin D-3 is characterized with an increase in current during the irradiation.