The long term goal of this project is to determine at a molecular level the structural basis for the known physiological function and mechanism of action of Transferrin (TF). We hope to achieve this goal through crystallographic studies on Tf. There are two mainlines of research which we propose to undertake. The first is to extend the structure of hen ovo-Tf to 2.5 A resolution. The second line will involve the use of various crystallographic probes in order to answer some basic questions regarding structure-function relationships in the Tf's. This will involve looking at abortive complexes of hen ovo-Tf viz. protein saturated with metals other than iron and anions other than carbonate. We propose to study the structure of partially aglycosylated Tf as well. Both lines will be pursued using single crystal X-ray diffraction methods as these have been applied to protein structures .