The Structure of Bound Water and Refinement of Acid Metmyoglobin
The structure of myoglobin as determined from x-ray diffraction data was first reported by Kendrew et al. (1). More recently, Takano (2) described the acidmet and deoxy forms, and Phillips (3) described the oxy form. In these x-ray structures, the positions of the hydrogen atoms cannot be described, but they are important factors in determining the interactions of the heme with its environment. Neutron diffraction work, done in this laboratory, has demonstrated that hydrogen and deuterium positions can be located (4). In addition to the localization of H and D, neutron diffraction provides a unique method for studying the water structure because of the strong scattering ability of D2O. The scattering factor of deuterium is nearly twice as large as that of hydrogen, and it increases the visibility of water molecules in Fourier maps, so that in a neutron map a water molecule appears about three times as strong as in an equivalent electron-density map. Detailed results of the neutron diffraction analysis of carbonmonoxy myoglobin (5) and oxymyoglobin (6), and the initial results on acid metmyoglobin (7) have been reported. The reciprocal-space refinement of acid metmyoglobin and in particular the details of the water structure and hydrogen exchange are presented here.
KeywordsTemperature Factor Hydrogen Exchange Residue Number Amide Hydrogen Bound Water
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