Conformational influence on the hopping conductivity in pig insulin.

Abstract

The ac conductivity of pig insulin has been reported previously [Y.-J. Ye and J. Ladik, Phys. Rev. B 48, 5120 (1993); Int. J. Quantum Chem. 52, 491 (1994)]. Now we have calculated in the ab initio scheme using Clementi's minimal basis set and the random-walk theory of Lax and co-workers the ac conductivity in another conformation that occurs in the same crystal. The results confirm the conclusions of the previous papers, that is, native proteins can be good amorphous semiconductors if they are doped. The comparison of the results of the two conformations of pig insulin shows that the ac conductivity changes two orders of magnitude in the frequency range that corresponds to the time period of the elementary steps of chemical reactions (\ensuremath{\omega}>${10}^{10}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$) when the three-dimensional structure changes. However, it does not change significantly in the low-frequency range (\ensuremath{\omega}${10}^{4}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$). The conclusion is that in the high-frequency range insulin would change both the ac conductivity of itself and its receptor if it binds to a receptor. Thus insulin might change the electron transport in the receptor when it expresses its biological activity.