In order to study electronic state of protein-biomolecular system, we started to develop a Molecular Orbital(MO) calculation system on Grid environment.

This system realizes MO calculation for large scale biosystem such as Estrogen receptor and DNA. (Figure 1) Analysis of electronic state gives a lot of basic information to not only drugs and materials design but also guidelines for medical treatment. For the Estrogen dimer and DNA system, the role of the dimer and waters became clear. Dimer fixs coordinate position and direction. Waters shield Coulomb force and play as glue connecting DNA and Estrogen dimer.

Grid technology is indispensable to large scale MO calculation.