The enzyme hen egg-white lysozyme was one of the first macromolecular structures to be solved using X-ray diffraction techniques in the 60's   . The results of extensive studies on the binding of heavy atom complexes to lysozyme, myoglobin and hemoglobin have been published by Blake . Of particular interest was the fact that Iridium and Osmium both formed isomorphous derivatives when introduced as and ions into tetragonal () crystals of lysozyme (cell dimensions Å).
In these studies it was reported that the Iridium and Osmium complexes were taken up in the same position as that occupied in the mercuriiodide derivative. The site is on a two-fold axis running along the () direction in the lattice and the included ion was bound by two Arg13 residues from symmetry related protein molecules.