Abstract: On the basis of zero differential overlap and the monopole model, the interaction energies between two insulin molecules have been calculated when they get close each other. It is shown that the energy of the whole system decrease continually as two molecules approach at a definite direction. The energy decreases until the stable position is arrived, namely θ= 0°, d= -0.5Å. The calculated data are very similar to the position the crystal structure data present. If they are forced to close each other, the energy, especially the repulsive force will increase rapidly. The total interaction energy and its constitutes at different distance and orientation are analysed.

Key words: Insulin, Interaction energy, Stable position