Technology Operations Core 4: Abstract Technology Operations Core 4 (TOC4) integrates the method of X-ray footprinting mass spectrometry (XFMS) into the ALS-ENABLE resource, providing resource users with a solution state structural biology method that is highly complementary to macromolecular crystallography (MX, TOCs1&3) and small angle X-ray scattering (SAXS, TOC2). XFMS is an in situ hydroxyl radical (•OH) labeling method based on well-established solvent accessibility protocols similar to Fenton chemistry and hydrogen deuterium exchange, sharing the same liquid chromatography-mass spectrometry (LCMS) data collection platform. The method provides residue-level structural information on proteins and/or nucleic acid in the solution state, and can be used for time-resolved studies and on complex mixtures of proteins in solution. Because of its versatility, the method has been especially valuable in obtaining structural and kinetics information that is highly complementary to the information obtained using the other more well-known structural biology methods such as MX an SAXS. The XFMS method has a vibrant, growing user base, has advanced substantially over the previous decade in automation and throughput, and is now close to the same level of routine use as MX and SAXS. In the last four years in particular, the instrumentation developed as part of a current NIGMS R01 award has significantly advanced the throughout and accessibility of the method for the larger biomedical community, including the development of an automated liquid sample delivery system, a remote-accessible beamline control interface, and automated LCMS data analysis. Through TOC4, we will make available our automated, high throughput, and hybrid spectroscopy- XFMS platform to ALS-ENABLE users through remote access, onsite and mail-in options. We will integrate information about XFMS and access to databases through the ALS-ENABLE website (als-enable.lbl.gov) so that users will have a single front-facing portal through which to learn about and access data from all the structural biology beamlines at the ALS. The integration of these technologies within the ALS-ENABLE resource will extend the structural biology capabilities at the ALS such that even more challenging biological systems can be studied, thus providing the national biomedical community with a powerful and increasingly versatile new tool for investigation of macromolecular assemblies.