The protein engineering is expected to bear fruitful products from the industrial and scientific aspects. It is entirely based on the three dimensional structure of proteins. The recent studies on the protein structures by X-ray suggest how to modify the protein by replacement of an amino acid residue into the other. The useful protein which has not been found in the natural world will be also produced by the protein engineering, inspecting the protein structure carefully. [J. Cryst. Soc. Jpn. 29, 38 (1987) ] .
