During the period of support of this research we have demonstrated the feasibility of our new method for the ascertaining of the locations of hydrogen atoms in molecules in crystals. We have applied the method to the enzyme, hen egg-white lysozyme, and have shown its ability to solve a problem concerning the relations between local structure and the binding of metal ions to this protein. Having demonstrated the method, and having developed suitable apparatus and techniques for its application, we have now turned our attention to use of our method for study of a number of problems, relative to protein structure, for the solutions of which the measurement of hydrogen atom coordinates provides important information. Such information is not available from x-ray diffraction studies of large molecules. Our method for obtaining it can provide a very useful tool for measuring the changes in conformations of enzymes and substrates that are important for enzymatic catalysis, for determining the role of bound metals in the biological functions of many types of proteins, for the study of the role of hydrogen bonding in fixing protein structure and function, and for the investigation of the role of water molecules in many processes mediated by proteins. Our new method employs electron paramagnetic resonance and electron proton double resonance spectroscopy of crystals of proteins with attached paramagnetic metal ions. The measured anisotropies of the proton-electron hyperfine interactions provide values of proton coordinates.
