[68] Benzophenone-ATP: A Photoaffinity Label for the Active Site of ATPases

This chapter describes the benzophenone-ATP that is used as a photoaffinity label for the active site of ATPases. The chapter outlines the methods, arguments in support of the use of benzophenone as a preferred photoactive moiety in the design of photoaffinity substrate analogs, referring specifically to 3'-O-(4-benzoyl)benzoyl-ATP (benzophenone-ATP or BzATP). One of the most attractive aspects of BzATP as a photoaffinity probe, in addition to the unique photochemical properties of benzophenone, is the relative ease with which it is synthesized. These factors should help to encourage the use of BzATP (and other “Bz-ligand” derivatives) as being well suited for studies of ATP-utilizing enzymes. The chapter reviews the underlying logic pertaining to the use of benzophenone-derivatized ligands for receptor domains on diverse biological macromolecules in an aqueous reaction medium. Thus, the introduction of a new photoaffinity probe into the arsenal of useful molecular tools employed by the biochemist must await its successful application by other laboratories.