The objective of this research is to determine the structures of oxy- and deoxyhemerythrin as a basis for understanding how the hemerythrin system transports and stores oxygen in certain marine organisms. The methods to be used are those of single crystal X-ray diffraction, including crystallographic refinement of the models based on multiple isomorphous replacement phases or derived from the rotation function. We also hope to determine the structures of oligomers of hemerythrin other than the octamer in order to study differences in the interactions holding the subunits together. The overall goal of these crystallographic studies is to obtain structural data for comparison with other types of information concerning 02 binding proteins to better understand the biochemical aspects of oxygen transport.