Theory of hopping conductivity in pig insulin

The ac conductivity for a native protein, pig insulin, was calculated in the ab initio scheme using Clementi’s minimal basis set. The hopping centers and ‘‘main residue’’ of an orbital are defined. It is assumed that the hopping events of charge carriers happen among these centers of main residues. The analysis of primary hopping events shows that there might be a relationship between the distribution of the hopping centers and the biochemical activity of insulin, and that the disulfur bridges of insulin have particular relevance for the ac conduction. The formulas for calculation of the ac conductivity of proteins are given. The results show that the curve of the frequency versus ac conductivity of pig insulin lies in the range of some typical inorganic amorphous conductors and confirm that proteins if doped are amorphous conductors. Finally, the possibility of direct comparison of the theoretical results with experiments is discussed.