Lawrence Berkeley National Laboratory

Metalloenzymes use the environment around the metal site to manage substrate interactions with the metal in order to effect efficient and specific catalysis under ambient conditions. Use of fs X-ray pulses from an XFEL allows to follow such reactions at room temperature (RT) without inherent radiation damage to the active site during the X-ray measurement [1-3]. We developed an approach employing simultaneous X-ray crystallography (XRD) and X-ray Emission (XES) techniques using fs XFEL-pulses [4,5] that provides complementary information: detailed information about changes in the electronic structure of the catalytic metal (XES), and the geometric changes of the metal site and the entire protein (XRD). In this experiment we used fs XFELs-pulses for RT studies of redox active metalloenzymes to capture reaction intermediates and expand time resolved studies of proteins at XFELs beyond photo-activated systems to chemically triggered systems. The main objective of this beam time was to test a novel sample delivery setup that was designed to allow drop on demand sample delivery combined with oxygen gas incubation of the individual sample drops prior to X-ray probing. We intended to test a new geometry, drop-on-wheel, which differs from our previously established drop-on-tape setup [6] and promises easier installation and operation. We included several important metalloenzymes, (ribonucleotide reductase, hydrogenase and methane monooxygenase) in this experiment to test this approach. Initial results from these tests are reported here.