Experimental observation of bonding electrons in proteins.

We demonstrate with two examples the success and potential of recent developments in x-ray protein crystallography at ultra high resolution. Our preliminary structural analyses using diffraction data collected for the two proteins crambin and savinase show meaningful deviations from the conventional independent spherical atom approximation. A noise-reduction averaging technique enables bonding details of electron distributions in proteins to be revealed experimentally for the first time. We move one step closer to imaging directly the fine details of the electronic structure on which the biological function of a protein is based.