This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Prostaglandin (PG) D2 is produced in a variety of tissues as a major prostanoid. In the central nervous system, PGD2 is known to regulate various body reaction, such as inducing sleep, body temperature, hormone release. Among the two types of Prostaglandin D2 synthese (PGDS), hematopoietic PGDS (H-PGDS) is localized in Th2 cells and mast cells in a variety of tissues, which requires glutathione (GSH) for the catalytic reaction. It is reported recently that the GSH binding site (catalytic pocket) is activated by the Ca2+ ions. We will compare Ca XAS in the presence and absence of GSH. In this proposal, we study the structural and functional roles of Ca in the enzymatic reaction. To probe the functional Ca binding site, we will perform Ca XAS studies on H-PGDS samples having 1 Ca per dimer H-PGDS samples expressed and purified from E. coli. Possible functional roles of other divalent metals and transition metals will also be explored. Additionally, we plan to carry out SAXS to study the bonding form of GSH in the binding pocket.